High efficiency leds and led lamps

ABSTRACT

In various embodiments, lighting systems include an electrically insulating carrier having a plurality of conductive elements disposed thereon, a light-emitting array, and at least one power source. The light-emitting array is disposed over the carrier and includes a plurality of light-emitting strings, each light-emitting string comprising a plurality of electrically connected light-emitting diodes (LEDs). Each LED has at least two electrical contacts, and each electrical contact is electrically connected to a conductive element by a conductive adhesive and/or a solder. The power source provides power to the light-emitting strings.

PRIORITY CLAIM

This application claims priority to commonly-owned U.S. ProvisionalPatent Application Ser. No. 61/221,046 filed 27 Jun. 2009 under thetitle “IMPROVED LEDS AND LAMPS,” incorporated by reference in itsentirety.

TECHNICAL FIELD

This application relates generally to light-emitting devices. Morespecifically, this application relates to arrays of light-emittingdiodes (“LEDs”) and lamps and fixtures comprising arrays of LEDsfabricated and operated in a mode having improved efficiency and reducedcost.

BACKGROUND ART

Increasing the efficiency of general lighting is one of the main ways toreduce global power consumption. About 25% of the electrical powerproduced in US is used for lighting. Since conventional lamps are notquite inefficient, increasing the efficiency of general lighting willyield major energy-saving benefits worldwide. In the United States, theU.S. Department of Energy (DOE) estimates that power consumption forlighting could be reduced by 50% simply by replacing conventional lampswith solid state lamps.

Currently, general lighting is achieved using a wide variety of lamptypes: so incandescent, fluorescent, tungsten halogen, sodium, clearmetal halide, etc.

The most commonly used types of lamps are incandescent and fluorescent,with incandescent lamps being most widely used in residential settings.These types of lamps are available in many different forms and withdifferent total lumen outputs and color characteristics. Two otherimportant lighting parameters are the Color Temperature (CT) and theColor Rendering Index (CRI). The CT is a measure of the lamps“whiteness”, its yellowness or blueness, or its warmth or coolness. CRIis a measure of the quality of the light; in other words how accuratelydo colors appear when illuminated with the lighting source. The highestCRI is 100 and typically incandescent lamps have the highest value ofCRI, as their emission spectrum is basically identical to a black bodyradiation spectrum. Other types of lamps may have a lower CRI. It ispossible for different lamps to have the same color temperature but adifferent CRI.

The economics of lighting has three main variables—light (lumens, lm),power (watt, W), and cost (dollar, $). Luminous efficacy is the amountof light produced per unit of electrical power (lm/W). Purchase costefficacy is the amount of light produced per dollar (lm/$). Forreference, incandescent lamps have a luminous efficacy of about 8-15lm/W. The purchase cost may also be referred to as the first cost.

For users of light, the cost of lighting has two components, the first(purchase and installation) costs, and the cost of the electricity(operating cost). While incandescent and fluorescent lamps have arelatively high purchase cost efficacy, their luminous efficacy andoperating costs are relatively high because of their low luminousefficacy. In continuous operation, an incandescent lamp costs about$90-$120 per year and must be replaced after approximately 1000 hours(1.5 months). In normal residential use (about 14 hours/week of on time)incandescent lamps cost about $8/year to operate and must be replaced inabout 18 months. Operating cost may also include the cost to changelamps, in addition to the electricity cost.

In order to reduce energy consumption associated with general lighting,new types of lamps are being investigated. One of the new types that arereceiving interest because of its potentially relatively higherefficiency is a light emitting diode (LED)-based lamp. LEDs havedemonstrated luminous efficacies over a wide range, from about 20 toabout 140 lm/watt (here LED means a package containing an LED die; in afew cases a package may have several discrete die mounted in onepackage).

LEDs may emit light in one wavelength range, for example red, amber,yellow, green, blue, etc. or may be designed to emit white light. Ingeneral single color LEDs are made by using a material whose bandgapemits light in desired the wavelength range. For example, yellow, amberor red light may be produced using LEDs formed from the AlInGaP materialsystem. Blue, UV and green LEDs may be formed, for example, using theAlInGaN material system. In other examples, single color LEDs may beformed using a combination of a LED emitting light of a first wavelengthand a light conversion material, for example a phosphor, that absorbs aportion or all of the first emitted wavelength and re-emits it at asecond wavelength.

White LEDs may be produced by a number of techniques, for example bycombining an LED with one or more light conversion materials such asphosphors, here referred to as a phosphor-converted white LED, or bycolor no mixing of multiple LEDs emitting different colors (a typicalcolor mixing arrangement may comprise a red, a green and a blue LED butother combinations may be used) or by combinations of one or morephosphor-converted LEDs and one or more direct emitting LEDs, that isLEDs that do not comprise a phosphor. LEDs may have a high CRI (>90) anda warm CT, producing a quality of light similar to that of anincandescent lamp. The CT and CRI of an LED depend on the spectraloutput of the LED as well as the characteristics of the phosphor. Warmcolors and a high CRI typically require more emission in the redwavelength range, and phosphor efficiency and the human eye'ssensitivity in the red wavelength range is relatively lower than that ingreen-yellow range. Thus LEDs with a warm color and/or a relatively highCRI typically have a relatively lower luminous efficacy than LEDs with acool color and/or a relatively low CRI.

Conventional LED lamps, also called prior art LED lamps, have improvedluminous efficacy (about 40 to about 70 lm/W) and long lifetime (about30,000 to about 50,000 hours) compared to incandescent lamps. However,conventional LED lamps are very expensive (about $80 to about $130 perlamp) and thus, even though the electricity costs are typically about ¼to about ½ that of incandescent lamps, the high first cost (also knownas the purchase cost) is sufficient to prevent widespread adoption. ALED lamp comprises the LEDs and any necessary electronics, optics,thermal management systems and housing to permit it to operate ongenerally available AC power.

Two key problems with prior art LED lamps are (1) the luminous efficacyof the LED lamp is only about 50-70% of that achievable with anindividual LED and (2) the very high first cost. Although higher firstcosts can be mitigated by reduced operating costs and longer lifetimes,customers' price expectations often pose psychological barriers tosales. The DOE predicts that a payback time of no more than 2 years(less than two incandescent bulb lifetimes (IBL)) will be required toaccelerate adoption of LED lighting, Meaningful energy conservation ispossible only with widespread adoption of LED lighting. The cost elementwith the biggest impact on the payback time is the first cost—forconventional LED lamps it is a virtually insurmountable obstacle. Forexample, the current approximately $100 lamp first cost leads to apayback time of about 10 years or about 7 IBL.

Payback time may be calculated in many different ways, but two main onesare the out-of-pocket approach and amortization approach. In the out ofpocket approach, payback occurs when the cost of the LED lamp plus itselectricity cost equals the cost of the incandescent lamp or lamps plusits electricity cost. This calculation includes the purchase of anadditional incandescent lamp at the end of the payback time, to reflectthe fact that going forward one would need a new lamp after the previousincandescent lamp burned out, whereas the LED lamp would keep operatingbecause of its significantly longer lifetime. The amortization paybacktime approach amortizes the lamp cost over its entire lifetime, thusresulting in shorter payback times than the out-of-pocket approach. Theout-of-pocket approach may be more realistic and representative of howsuch decisions are made and is the calculation mainly used for paybacktimes in this document.

The lower luminous efficacy of prior art LED lamps compared toindividual LEDs is caused by a number of factors including the reductionof luminous efficacy of the individual LEDs under actual operatingconditions, the cost of assembling multiple LEDs into a lamp, theoptical losses associated with the use of multiple LEDs in the lamp andfixture, the efficiency losses associated with the power converter andLED driver and the further reduction in efficiency and lifetime of allcomponents from high operation temperatures, which in turn is a resultof high junction temperatures and high current densities at which LEDdie are operated to achieve the desired total lumen output Each of thesefactors will be discussed in detail below.

Very few individual LEDs produce enough light to be used individuallyfor general lighting. In most cases LED lamps contain a relatively largenumber of individual packaged LEDs, on the order of about 10 to aboutseveral hundred. It is understood that a large number of individuallypackaged LEDs increases the lamp cost as it then includes the packagecost for each LED as well as the assembly cost of putting all of theLEDs together in the lamp. Thus the current industry direction and DOEroadmap is to drive the LEDs at higher currents in order to generatemore light from each LED while minimizing the required number of LEDs.

The problem with this approach is that the luminous efficacy of anindividual LED decreases strongly with increasing drive current (for agiven LED die size one may use a value of current and when comparing LEDdie of different sizes, one may choose to use either current or currentdensity). The relatively high luminous efficacies demonstrated for priorart LEDs are achieved by operating at very low current (currentdensity). At the low currents used to achieve the high luminous efficacynumbers, these devices produce relatively little light; certainly notenough to replace a single incandescent lamp. For example individualLEDs may produce, at these current levels, about 5 to about 200 lumens.Operation at higher current produces more light, but at the expense ofsignificantly reduced luminous efficacy. For example, FIG. 1 shows aplot of luminous efficacy (top graph) and total light output (bottomgraph) as a function of drive current for several state of the art LEDs.In particular, there are three curves in each graph of FIG. 1 showingcool white LEDs made by Lumileds (K2 star package, dash lines), Cree(XLamp XR-E, dotted lines), and Luminus Devices (SST-90, dash-dottedlines). The data for the brightest bins for each device is used. Eachcurve has a thick solid part which represents the driving conditions atwhich devices are designed to operate. It is clear that the luminousefficacy decreases rapidly with increasing current, and that theluminous efficacy within the designed operation range is about half ofthe peak luminous efficacy that could be achieved at low currents.

The data shown in FIG. 1 is taken with the LEDs maintained at 25° C. Inactual operation maintaining such a low temperature is not possible andas the current increases, the LEDs operate at significantly highertemperatures, in the range of about 50° C. to about 100° C., whichcauses the luminous efficacy to drop further. Advanced packagingtechniques may be utilized to improve the heat removal and slow thejunction temperature rise; nevertheless, the luminous efficacy of thesame LED at high currents is almost always lower than that at lowcurrents in actual operation.

Another problem with the conventional LED lamp approach of using highcurrents (current density) is that the temperature rise associated withthis mode of operation decreases the lifetime of an LED. The LEDlifetime is generally referred to as the time period during which thetotal light output of an LED decreases to some percentage, typically70%, of its initial light output level (LEDs do not typically burn out,but instead have a gradual reduction in brightness). Driving an LED atrelatively high current densities and junction temperatures causesdegradation mechanisms to accelerate. A specific example of this isshown in FIG. 2 taken from DOE document PNNL-SA-51901, April 2007,Thermal management of white LEDs. One can see that for a typicalGaN-based LED the lifetime is about 40,000 hours when the junctiontemperature is about 63° C. (curve 136) and decreases to about 14,000hours when the junction temperature is about 74° C. (curve 138). Itshould also be noted that as the brightness decreases, the luminousefficacy is also decreasing, so a longer-lived LED may have a higherluminous efficacy and thus may have a lower cost, over its lifetime.

Because these LEDs are designed to operate at high current, the packagemust be designed to manage the relatively large amount of heat (about 1to about 5 watts) generated when the LED is operated at relatively lowerluminous efficacy (at high currents). Such packages are expensive, thusreducing the purchase cost efficacy. FIG. 3 shows the luminous efficacy(top graph) and the purchase cost efficacy (bottom graph) as a functionof lumen output (the lumen output is varied by changing the drivecurrent, as shown in FIG. 1) for the same devices as in FIG. 1. The sameline types are used for each device and the thick solid part of eachcurve represents the designed operating range. It is clear from thisdata that the purchase cost efficacy (lm/$) increases rapidly withincreased lumen output but this is at the expense of luminous efficacy.For example, for the Luminus Devices SST-90, a purchase cost efficacy ofabout 40 lm/$ is only achieved at a relatively low luminous efficacy ofabout 60 lm/watt, about half the value achieved at very low currents. Atlow currents, where the luminous efficacy is about 120 lm/W, thepurchase cost efficacy drops to only about 10 lm/$.

As discussed above, a prior art LED lamp contains a relatively largenumber of LEDs. FIG. 4 shows a schematic of an exemplary prior art LEDlamp. Each packaged LED 142 is mounted on a carrier or circuit board 141and coupled with interconnects 144. The lamp housing 146 may alsocontain the power converter (to convert the 120VAC input to a DC levelsuitable for the LED driver and the LED driver (together shown as 148,inside housing 146) that provides a controlled current to the LEDs,appropriate thermal management systems including heat sinks 150, and anoptical system 140 to combine and diffuse and/or direct the lightemitted from the individual LEDs into a desired profile exiting the lampand a base 152.

LED lamp manufacturers must purchase multiple LEDs and assemble andintegrate them on the circuit board. This can be relatively expensive,and the cost increases when using higher and higher power LEDs. Inaddition to more expensive LED die, the LED package cost increases aswell. As the LEDs are designed to operate at higher and highertemperatures, the packages for such LEDs become more complex and moreexpensive, in some cases costing more than the LED die itself. Asdiscussed above, the luminous efficacy decreases at high current levelswhere the LEDs are designed to be operated. Thus the LED package must bedesigned to handle the large amounts of heat generated when the LED isoperating at the relatively lower luminous efficacy of the operationpoint. Such packages are expensive, and the need to use multiple suchpackages in the lamp significantly increases the lamp cost. Associatedwith this are the cost of the carrier or circuit board and the cost ofattaching the LED packages to the circuit board or carrier, for exampleusing solder. The lamp cost is further increased because of the need foradvanced thermal management systems required by operation at sub-optimalluminous efficacy values. Such thermal management systems are oftenpassive, including for example metal core circuit boards, heat sinks andheat radiating fins, but in some cases may even include an active devicesuch as a fan. All of these factors act to decrease the LED lamppurchase cost efficacy, increase the total cost/unit time and decreasethe lifetime of the lamp.

Referring again to FIG. 4, one can see that the light emitted from thelamp must traverse a large number of interfaces with differentrefractive indices. Starting with the LED die, the light passes from thesemiconductor die through the encapsulation of the package, a region ofair, the lens/diffuser system 140 and then out of the lamp. Thus thelight must traverse at least 4 interfaces. Each interface is associatedwith optical losses resulting from the difference in refractive indicesof the materials forming the interface. Even at a 00 incident angle partof the incident light may be reflected back and potentially absorbed andconverted to heat. The amount of the light reflected back depends on thevalues of refractive indices of the materials forming the interface—thecloser they are, the less light that may be reflected back. At a typicalsemiconductor (for example Si, GaAs, GaP or GaN)/air interface up toabout 30% of visible light may be reflected back, as the ratio ofrefractive indices between semiconductor and air is typically around 3.

Another optical loss mechanism that occurs at the interface is totalinternal reflection. According to Snell's law, light incident upon aninterface is refracted or reflected depending on the angle of incidenceand the index of refraction on either side of the interface according tothe equation n1 sin θ1=n2 sin θ2 where n1 and n2 are the index ofrefraction on either side of the interface, θ1 is the incident angle andθ2 is the refracted angle. A schematic of this is shown in FIG. 5 inwhich material 1 is identified as 164, material 2 is identified as 162and the interface between material 1 and material 2 is identified as160. 165 identifies the normal direction to the interface, 166represents the angle of incidence in material 1 and 168 represents therefracted angle in material 2. When the angle of incidence is largeenough, no light is refracted, but instead all light is reflected backinto material 1. This situation is called total internal reflection(TIR) and may be the cause of large optical losses. For example, usingtypical values for semiconductors and encapsulants, all light incidentupon that interface at an incident angle greater than about 27° will betotally internally reflected. TIR light will suffer absorption losseswithin the die as it is reflected from various interfaces, leading toreduced light output and increased generation of heat. For an example ofa simple rectangular LED die, only about 28% or less of the lightgenerated within the LED die may escape the die, into the surroundingencapsulant. A great deal of work has gone into improving the lightextraction efficiency of the die within the package/encapsulant. Asdiscussed above, the LED lamp includes at least three (3) otherinterfaces at which Snell's law applies and at which further opticallosses may occur.

Additional optical losses may also occur in lamps comprising a pluralityof individual LEDs, for example packaged LEDs, arranged on a circuitboard or carrier because of the increased etendue of the optical system(etendue refers to how “spread out” the light is in area and angle). Ina given lamp or fixture design, one can only capture all of the lightfrom the light source if the etendue of the light source is below acertain value (that value depends on the optical design of the lamp orfixture). In other words, as the dimensions of the light emitting areaincrease (the etendue increases) it becomes more difficult to focus anddirect the light into a desired pattern without optical losses.

Lamps may also suffer further optical losses when put into a fixture.This is more significant for incandescent and fluorescent lamps thatemit light in a relatively omnidirectional pattern. LEDs emit light in adirection pattern and thus LED lamps may suffer less light losses wheninstalled in a fixture. Typically the optical efficiencies associatedwith light loss from prior art LED lamps in a fixture are in the rangeof about 80%.

In some embodiments the LED lamp may use 120VAC for its input source andthis may be converted to DC to drive the LEDs in a constant currentmode. In this situation electronics, also called the driver, may berequired to convert the 120VAC to a DC voltage and current suitable forthe LEDs.

The electronics efficiency is affected by its output voltage andtypically increases as the output voltage approaches the input voltage.For example FIG. 6 shows the efficiency of a National SemiconductorLM3445 Triac LED driver as a function of output voltage for an inputvoltage of 115VAC. As the output voltage increases from about 33 voltsto about 47 volts (corresponding to about 10 and about 14 GaN-based LEDsin series, respectively), the driver efficiency increases from about 85%to about 90%. LEDs typically operate in the range of about 2.5 to about4 volts and when the number of the LEDs in the lamp is relatively low,the difference in LED voltage and the input voltage is relatively large,resulting in a relatively low efficiency. The electronics efficiency mayalso be a function of temperature, decreasing with increasingtemperature. In some embodiments, the electronics efficiency may beginto decrease when the ambient temperature rises above about 500 C. FIG. 7shows the power conversion efficiency of an exemplary 20 watt AC/DCconverter (Recom RAC20-S_D_TA series) as a function of temperature. Ascan be seen, the power conversion efficiency decreases significantlyover about 50° C. In the typical operating temperature range for priorart LED-based lamps (about 60° C.) the power conversion efficiency hasdecreased by almost 50% for this particular power converter.

Typically the efficiencies associated with present day electronics(drivers) are in the range of about 85%. While the electronicsefficiency may be able be improved with respect to both output voltageand dissipated heat for conventional LED lamps, this may lead tounacceptable increases in the electronics form factor and cost.

As discussed above, prior-art LED lamps comprising one or more packagedLEDs driven at relatively high currents and high current densitiesgenerate significant heat because of their low luminous efficacy. As thetemperature is increased, the light output of LEDs is reduced, thusfurther reducing the luminous efficacy. The LED and driver lifetime isalso reduced as potentially is the efficiency of the driver. FIG. 8shows a table presenting the percentage of input power that is convertedto either heat (IR+conduction+convection) or light for exemplaryincandescent and fluorescent lamps and exemplary prior art LED lamps. Itcan be seen that the LED lamps produce significantly more visible lightpower than incandescent lamps, but still produce a significant amount ofheat which must be managed appropriately. Typically this means higheroperating temperatures and more expensive packaging and thermalmanagement techniques.

The overall luminous efficacy of a LED lamp may be expressed as where isthe luminous efficacy of the LED and is a function of temperature, isthe optical efficiency and is the efficiency of the driver electronicsand is a function of ambient temperature. For example, the LEDs fromdotted and dash-dotted curves in FIG. 1 which may have a low currentluminous efficacy of about 135 lm/W, in typical prior art operationconditions may have a luminous efficacy of about 75-85 lm/W. Usingvalues of 85% for both the optics and driver efficiency, the prior artLED lamp in operation would then have an overall luminous efficacy of 54lm/W. Note that this does not include any temperature effects. Typicaldesign guides recommend an 85% derating for the LED related totemperature, yielding a temperature-adjusted overall LED lamp luminousefficacy of only about 46 lm/W.

Alternatively the LED lamp efficiency may be described as the product ofnon-temperature sensitive factors for the LED, the optics and the driverand a temperature factor, which may also be called the thermalefficiency; ηlamp=ηLED*ηDriver*ηOptics*ηThermal. FIG. 9 shows current(2008) and 2015 target values for these four efficiencies as determinedby the U.S. Department of Energy (Multi-Year Program Plan FY'09-FY'15,Solid State Lighting Research and Development, March 2009). In FIG. 9,the efficiency of the LED is expressed as a percentage, that is, thelight output power divided by the input electrical power. For referencea neutral white LED efficiency of about 30% corresponds to a LEDluminous efficacy of about 90 lm/W. From this table it can be seen thateven though advances have been made in conventional LED lamps, theoverall efficiency of conventional LED lamps is only about 17%.

In spite of all of these issues, the overall luminous efficacy of priorart LED lamps is still higher than that of incandescent lamps. However,conventional LED lamps are very expensive ($80-$120 per lamp) and thus,as discussed previously, even though the electricity costs are typicallyabout ¼ to about ½ that of incandescent lamps, the high first cost issufficient to prevent widespread adoption.

There is accordingly a general need in the art for techniques anddevices that simultaneously provide high efficiency, high brightness andlow cost in LEDs, LED lamps and LED lighting systems.

SUMMARY OF INVENTION

In the following description and claims, the terms “comprise” and“include,” along with their derivatives, may be used and are intended assynonyms for each other and mean that addition of unnamed extra elementsis not precluded. In addition, in the following description and claims,the terms “coupled” and “connected,” along with their derivatives, maybe used.

As used herein, the term “connected” may be used to indicate that two ormore elements are in direct physical or electrical contact with eachother. The term “coupled” may mean that two or more elements are indirect physical or electrical contact. However, “coupled” may also meanthat two or more elements are not in direct contact with each other, butyet still co-operate or interact with each other. For example, “coupled”may mean that two or more elements do not contact each other but areindirectly joined together via another element or intermediate elements.

As used herein, the terms “on,” “overlying,” and “over” may be used inthe following description and claims. “On,” “overlying,” and “over” maybe used to indicate that two or more elements are in direct physicalcontact with each other. However, “over” may also mean that two or moreelements are not in direct contact with each other. For example, “over”may mean that one element is above another element but not contact eachother and may have another element or elements in between the twoelements. It should be noted that “overlying” and “over” are relativeterms that include layers located beneath a substrate when the substrateis turned upside down.

As used herein, the term “group III” elements indicates the elementsfound in what is commonly referred to as group III of the periodictable. For example, boron (B), aluminum (Al), gallium (Ga), and indium(In) are group III elements. Similarly, the term “group V” elementsindicates the elements found in what is commonly referred to as group Vof the periodic table. For example, nitrogen (N), phosphorus (P),arsenic (As), antimony (Sb), and bismuth (Bi) are group V elements.

A first aspect of the present invention is light-emitting devicescomprising a plurality of relatively small LED units operating at nearpeak efficacy. In some embodiments of this aspect the LED units may beorganized in an array, wherein such array may be a regular array, forexample a rectangular array comprising rows and columns of LED units. Inother embodiments of this aspect, the array may have other shapes, ormay not be a regular array. Such light emitting devices may be referredto as a light engine or LED array.

In some embodiments of this aspect, the LED units of the light emittingdevice are operated within 30%, or within 20% or within 10% of theirpeak efficiency value. In some embodiments of this aspect, the number ofLED units is sufficiently large to produce a total light output of atleast 300 lumens, or at least 500 lumens, or at least 1000 lumens orgreater. In some embodiments the number of LED units in the array may beat least 4, or at least 25, or at least 50, at least 100 or at least150. Each light emitting device provides the required amount of lightfor a particular application. The amount of light is varied by changingthe number of LED units, rather than changing the current drive in theLEDs, as is done in prior art LED lamps.

In some embodiments of this aspect, each LED unit of the light emittingdevice is operated at a relatively low current or current density, suchthat the luminous efficacy of the LED unit is within 30%, or within 20%or within 10% of its peak efficiency value. In some embodiments of thisaspect each LED unit is operated with a current density that does notexceed 0.75 A/mm2, or does not exceed 0.55 A/mm2 or does not exceed 0.4A/mm2 or does not exceed 0.10 A/mm2. In some embodiments of this aspecteach LED unit may have an area no larger than 1 mm2, or no larger than0.5 mm2, or no larger than 0.25 mm2 or no larger than 0.05 mm2. In someembodiments of this aspect the current in each LED unit may not exceed100 mA, or may not exceed 50 mA or may not exceed 25 mA. In someembodiments of this aspect, the ratio of optical output power to totalpower dissipated by each LED unit (heat+optical power) may be greaterthan 25%, or greater than 30%, or greater than 40%.

Several merits arise from the present invention, relative to prior artLEDs. First, because each LED unit is operated at a relatively lowcurrent or current density, the luminous efficacy of the light emittingdevice is relatively closer to the peak value possible in comparison toprior art LEDs or LED lamps.

Second, because the luminous efficacy is relatively high, the amount ofheat generated by the light emitting device is relatively low comparedto prior-art LEDs. Thus the light emitting device of the presentinvention produces relatively more light and relatively less heat,resulting in relatively decreased purchase and operating costs. Thepurchase cost is lower because the reduced heat generation permits lesscostly packaging and thermal management systems. The operating cost isreduced because the luminous efficacy is higher and, because less heatis generated, heat-induced luminous efficacy losses and electricalefficiency losses are reduced.

In some embodiments of this aspect the LED units of the light emittingdevice may all be the same shape and size and have the same spacingbetween LED units, or the LED units may have different shapes and/orsizes and/or different spacing between LED units. In some embodiments ofthis aspect, the spacing between LED units within the array may be atleast 10 μm, or may be at least 30 μm, or may be at least 50 μm or maybe at least 100 μm.

In some embodiments of this aspect, all or a portion of the LED units ofthe light emitting device may be operated in a continuous mode; that isthe applied current is constant as a function of time for time periodsless than about 1 second or less than about 0.1 seconds. In otherembodiments of this aspect, all or a portion of the LED units may beoperated in a pulsed mode; that is the applied current varies as afunction of time for time periods less than about 1 second or less thanabout 0.1 seconds. In other embodiments of this aspect, a portion of theLED units may be operated in continuous mode and a portion may beoperated in pulsed mode. Pulse mode may also be called pulse widthmodulation.

In some embodiments of this aspect, the LED units of the light emittingdevice may be electrically coupled in series, in parallel, or in acombination comprising a string of one or more LEDs in series and aplurality of such strings in parallel. In other embodiments of thisaspect all of the LED units in the array may be electrically coupledtogether, and in other embodiments of this aspect, portions of the LEDunits in the arrays may be electrically coupled together resulting in aplurality of sub-arrays, each sub array comprising one or more LED unitswhich may be electrically coupled in series, in parallel, or in acombination comprising a string of one or more LEDs in series and aplurality of such strings in parallel.

In some embodiments of this aspect, a first terminal of thelight-emitting device may be coupled to only anodes of the LED units anda second terminal of the light-emitting device may be coupled only tocathodes of the LED units. In some embodiments of this aspect, a firstterminal of the light-emitting device may be coupled to the anodes of afirst portion of the LED units and to the cathodes of a second portionof the LED units. In some embodiments of this aspect, the light-emittingdevice may be operated with an AC or with a DC voltage.

In some embodiments of this aspect, each LED unit of the light emittingdevice may be operated with a DC voltage V (measure in volts) and adrive current I (measured in Amps) such that V>30*I, or such thatV>60*I, or such that V>100*I.

In some embodiments of this aspect, the light emitting device may beoperated with a DC voltage V (measure in volts) and a drive current I(measured in Amps) such that V>30*I, or such that V>60*I, or such thatV>100*I.

In some embodiments of this aspect, the LED units of the light emittingdevice may all emit a single color or may emit a plurality of colors. Inother words, the LED units may all emit light of a single spectraldistribution or color, or different LED units may emit light withdifferent spectral distributions or colors. In some embodiments of thisaspect, different LED units may emit light with different spectraldistributions or colors and this may produce light appearing as white tothe eye. For example, LED units emitting red, green and blue colors maytogether appear as white to the eye. In some embodiments of this aspect,each LED unit of the light emitting device may comprise one or moreactive regions in which carrier radiative recombination occurs. In LEDunits comprising more than one active region, each active region mayemit the same or different wavelengths and/or distributions of light.

In some embodiments of this aspect, all or a portion of the LED units ofthe light emitting device may be covered or partially covered by one ormore light conversion materials, for example phosphors that may absorball or a portion of the light emitted directly by one or more LED unitsand re-emit light with a different wavelength or color or spectraldistribution than that of the light emitted directly by the LED unit orLED units. In some embodiments the combination of light emitted directlyfrom all or a portion of the LED units and/or all or a portion of thelight emitted by the one or more phosphors or light conversion materialsmay produce light appearing as white to the eye, or as blue to the eye,or as green to the eye, or as red to the eye. However this is not alimitation of the present invention and in other embodiments, the lightmay appear to be any color to the eye.

In some embodiments of this aspect, light extraction features may beformed on the LED units of the light emitting device. Light extractionfeatures may increase the light extraction efficiency, resulting in arelatively higher LED unit luminous efficacy, and as a result, a higherlight emitting device luminous efficacy. In some embodiments of thisaspect the light extraction features may include surface roughening,photonic lattices, encapsulation or index-matching, anti-reflectioncoatings, mesa shaping, reflective contacts and other light extractiontechniques known to those in the art.

In some embodiments of this aspect, additional circuitry may be formedon a common or adjoining carrier, substrate or circuit board to provideadditional functionality to the light-emitting device, for example toprovide AC to DC power conversion or to provide a current source fordriving the LED units, or to permit independent or synchronizedoperation and control of a plurality of sub-arrays of LED units. Saidadditional circuitry may be formed in a monolithic or hybrid fashion.

In some embodiments of this aspect of the present invention thelight-emitting devices comprising an array of relatively small LED unitsoperating at near peak efficacy comprise individual packaged LEDsmounted on a circuit board or carrier.

In some embodiments of this aspect of the present invention thelight-emitting devices comprising an array of relatively small LED unitsoperating at near peak efficacy comprise individual LED die mounted on acircuit board or carrier.

In some embodiments of this aspect of the present invention thelight-emitting devices comprising an array of relatively small LED unitsoperating at near peak efficacy comprise individual LEDs units formedmonolithically on a common substrate. In an embodiment of this aspect inwhich additional circuitry is formed in a monolithic fashion, suchcircuitry may be formed on or from all or a portion of the layerstructure from which the LED units are formed, on or from all or aportion of an additional layer structure, on or from a common carriersubstrate or otherwise disposed on a common substrate.

A second aspect of the present invention are methods of fabricatinglight-emitting devices comprising an array of relatively small LED unitsoperating at near peak efficacy, said relatively small LED units formedin a hybrid fashion on a common substrate.

A third aspect of the present invention are methods of fabricatinglight-emitting devices comprising an array of relatively small LED unitsoperating at near peak efficacy, said relatively small LED units formedin a monolithic fashion on a common substrate.

A forth aspect of the present invention are light-emitting devicescomprising an array of relatively small LED units operating at near peakefficacy, a first portion of said relatively small LED units formed in amonolithic fashion and a second portion of said relatively small LEDunits formed in a hybrid fashion.

A fifth aspect of the present invention are LED lamps comprising anarray of relatively small LED units operating at near peak efficacy,said relatively small LED units formed in a hybrid fashion on a commonsubstrate.

A sixth aspect of the present invention are LED lamps comprising anarray of relatively small LED units operating at near peak efficacy,said relatively small LED units formed in a monolithic fashion on acommon substrate.

A seventh aspect of the present invention are LED fixtures or luminairescomprising one or more arrays of relatively small LED units operating atnear peak efficacy, said relatively small LED units formed in a hybridfashion on a common substrate.

A eighth aspect of the present invention are LED fixtures or luminairescomprising one or more arrays of relatively small LED units operating atnear peak efficacy, said relatively small LED units formed in amonolithic fashion on a common substrate.

BRIEF DESCRIPTION OF DRAWINGS

A further understanding of the nature and advantages of the presentinvention may be realized by reference to the remaining portions of thespecification and the drawings wherein like reference numerals are usedthroughout the several drawings to refer to similar components.

FIG. 1 is a plot of luminous efficacy and total light output as afunction of drive current for state-of-the-art LEDs;

FIG. 2 shows a relationship between operating temperature and lifetimefor LEDs;

FIG. 3 is a plot of luminous efficacy and total light output as afunction of light output for state-of-the-art LEDs;

FIG. 4 is a schematic illustration of an exemplary prior-art LED lamp;

FIG. 5 is a diagram of light incident on an interface;

FIG. 6 shows the relationship between output voltage and efficiency fora LED driver;

FIG. 7 shows the power conversion efficiency of an AC/DC converter as afunction of temperature;

FIG. 8 is a table listing the percentage of input power that isconverted to light and heat in various types of lighting;

FIG. 9 is a table listing current and 2015 target efficiency values forLEDs;

FIG. 10 is a schematic of examples of electrical configurations ofarrays of LEDs;

FIG. 11 is a schematic illustration of a structure of a light emittingdevice made in accordance with a first embodiment of the invention;

FIG. 12 is a schematic illustration of a structure of a light emittingdevice made in accordance with a second embodiment of the invention;

FIG. 13 shows the relationship of the cost of a kilolumen of light peryear produced by different lighting technologies as a function ofoperating time per week;

FIG. 14 shows payback time in years as a function of operating time forseveral LED lamps compared to an incandescent lamp;

FIG. 15 shows the relationship between luminous efficacy and lightoutput with different yield loss;

FIG. 16 is a schematic of examples of additional electricalconfigurations of arrays of LED in accordance with an embodiment of theinvention;

FIG. 17 is a cross-sectional view of a light emitting device made inaccordance with a third embodiment of the invention taken along sectionline 17-17 of FIG. 18;

FIG. 18 is a view of the light emitting device of FIG. 17 from the sideopposite the LED units;

FIG. 19 is a view of the light emitting device of FIG. 17 from the sidewhich emits light;

FIG. 20 is a cross-sectional view of a light emitting device at abeginning stage of manufacture in accordance with an embodiment of theinvention;

FIG. 21 is a cross-sectional view of the light emitting device of FIG.17 at an early stage of manufacture and of an embodiment of the lightemitting device of FIG. 20 at a later stage of manufacture and of across-sectional view of the light emitting device of FIG. 22 taken alongsection line 21-21 of FIG. 22;

FIG. 22 is a top view of the light emitting device of FIG. 21;

FIG. 23 is a cross-sectional view of the light emitting device of FIG.21 at a later stage of manufacture, and a cross-sectional view of thelight emitting device of FIG. 24 taken along section line 23-23 of FIG.24;

FIG. 24 is a top view of the light emitting device of FIG. 23;

FIG. 25 is a cross-sectional view of the light emitting device of FIG.23 at a later stage of manufacture;

FIG. 26 is a cross-sectional view of the light emitting device of FIG.25 at a later stage of manufacture;

FIG. 27 is a cross-sectional view of the light emitting device of FIG.26 at a later stage of manufacture;

FIG. 28 is a cross-sectional view of the light emitting device of FIG.27 at a later stage of manufacture;

FIG. 29 is a cross-sectional view of the light emitting device of FIG.28 at a later stage of manufacture;

FIG. 30 is a cross-sectional view of the light emitting device of FIG.29 at a later stage of manufacture;

FIG. 31 is a cross-sectional view of the light emitting device of FIG.30 at a later stage of manufacture;

FIG. 32 is a cross-sectional view of a carrier in accordance with anembodiment of the invention;

FIG. 33 is a cross-sectional view of the light emitting device of FIG.31 at a later stage of manufacture;

FIG. 34 is a cross-sectional view of the light emitting device of FIG.33 at a later stage of manufacture;

FIG. 35 is a cross-sectional view of a light emitting device made inaccordance with a fourth embodiment of the invention;

FIG. 36 is a cross-sectional view of the light emitting device of FIG.34 at a later stage of manufacture;

FIG. 37 is a cross-sectional view of the light emitting device of FIG.36 at a later stage of manufacture;

FIG. 38 is a top view of an entire wafer of light emitting devices madein accordance with an embodiment of the invention.

FIG. 39 is a top view of a light emitting device made in accordance witha fifth embodiment of the invention;

FIG. 40 is a top view of a light emitting device made in accordance witha sixth embodiment of the invention;

FIG. 41 is a cross-sectional view of a light emitting device made inaccordance with a seventh embodiment of the invention;

FIG. 42 is a cross-sectional view of a light emitting device made inaccordance with an eighth embodiment of the invention;

FIG. 43 is a cross-sectional view of a light emitting device made inaccordance with a ninth embodiment of the invention taken along sectionline 43-43 of FIG. 44;

FIG. 44 is a top view of the light emitting device of FIG. 43;

FIG. 45 is a cross-sectional view of a light emitting device made inaccordance with a tenth embodiment of the invention taken along sectionline 45-45 of FIG. 46;

FIG. 46 is a view from the light emitting side of the light emittingdevice of FIG. 45;

FIG. 47 is a cross-sectional view of the light emitting device of FIG.45 at an early stage of manufacture and of an embodiment of the lightemitting device of FIG. 20 at a later stage of manufacture;

FIG. 48 is a cross-sectional view of a second carrier in accordance withan embodiment of the invention;

FIG. 49 is a cross-sectional view of the light emitting device of FIG.47 at a later stage of manufacture;

FIG. 50 is a cross-sectional view of the light emitting device of FIG.49 at a later stage of manufacture;

FIG. 51 is a cross-sectional view of the light emitting device of FIG.50 at a later stage of manufacture;

FIG. 52 is a cross-sectional view of the light emitting device of FIG.51 at a later stage of manufacture;

FIG. 53 is a cross-sectional view of the light emitting device of FIG.52 at a later stage of manufacture;

FIG. 54 is a cross-sectional view of the light emitting device of FIG.53 at a later stage of manufacture;

FIG. 55 is a cross-sectional view of the light emitting device of FIG.54 at a later stage of manufacture;

FIG. 56 is a cross-sectional view of the light emitting device of FIG.55 at a later stage of manufacture;

FIG. 57 is a cross-sectional view of a light emitting device made inaccordance with an eleventh embodiment of the invention;

FIG. 58 is a cross-sectional view of a light emitting device made inaccordance with a twelfth embodiment of the invention taken alongsection line 58-58 of FIG. 59;

FIG. 59 is a view from the light emitting side of the semiconductorstructure of FIG. 58;

FIG. 60 is a schematic of a photonic crystal;

FIG. 61 is a cross-sectional view of the light emitting device of FIG.58 at an early stage of manufacture;

FIG. 62 is a cross-sectional view of the light emitting device of FIG.61 at a later stage of manufacture;

FIG. 63 is a schematic of an etch process;

FIG. 64 is a schematic of the etch process of FIG. 63 at a later stageof manufacture;

FIG. 65 is a cross-sectional view of the light emitting device of FIG.62 at a later stage of manufacture;

FIG. 66 is a top view of a light emitting device made in accordance withan thirteenth embodiment of the invention;

FIG. 67 is a cross-sectional view of a light emitting device made inaccordance with a fourteenth embodiment of the invention;

FIG. 68 is a cross-sectional view of the light emitting device of FIG.67 at a later stage of manufacture;

FIG. 69 is a cross-sectional view of a light emitting device made inaccordance with a fifteenth embodiment of the invention;

FIG. 70 is a schematic of a wafer of light emitting devices;

FIG. 71 is a distribution of luminous efficacy across a wafer;

FIG. 72 (A) is a top view of a light emitting device made in accordancewith a sixteenth embodiment of the invention and (B) is a distributionof intensity across a wafer;

FIG. 73 is a FIG. 69 is a cross-sectional view of a light emittingdevice made in accordance with an embodiment of the invention;

FIG. 74 is a schematic of a LED driver circuit;

FIG. 75 is a top view of a light emitting device made in accordance witha seventeenth embodiment of the invention;

FIG. 76 is a schematic of a light engine and optical element;

FIG. 77 shows a process flow for a prior-art LED lamp and a lightemitting device made in accordance with an embodiment of the invention;

FIG. 78 shows a comparison of the optical system for a prior-art LED anda light emitting device made in accordance with an embodiment of theinvention;

FIG. 79 is a cross-sectional view of a light emitting device made inaccordance with an eighteenth embodiment of the invention taken alongsection line 79-79 of FIG. 80;

FIG. 80 is a view from the light emitting side of the light emittingdevice of FIG. 79.

For simplicity of illustration and ease of understanding, elements inthe various figures are not necessarily drawn to scale, unlessexplicitly so stated. Further, if considered appropriate, referencenumerals have been repeated among the figures to indicate correspondingand/or analogous elements. In some instances, well-known methods,procedures, components and circuits have not been described in detail soas not to obscure the present disclosure. The following detaileddescription is merely exemplary in nature and is not intended to limitthe disclosure of this document and uses of the disclosed embodiments.Furthermore, there is no intention that the appended claims be limitedby the title, technical field, background, or abstract.

DESCRIPTION OF EMBODIMENTS

Embodiments of the invention generally provide a LED-based light system,for example a LED light engine, LED lamp or LED luminaire comprising aplurality of LED units operated at near peak efficiency.

In some embodiments of the present invention a light emitting device,also referred to as an LED array or a light engine, may comprise aplurality of relatively small LED units operating at near peakefficiency and at relatively low current. The LED units, also referredto as LEDs, may be coupled in a variety of configurations, as discussedbelow. The number of LED units comprising the light engine may beadjusted to produce a desired amount of light. For example, a LED unithaving an area in the range of about 0.0625 mm2 to about 0.25 mm2 mayoperate in the range of about 2.8 volts to about 3.3 volts with acurrent in the range of about 0.005 A to about 0.07 A and produce alight output in the range of about 1 lm to about 25 lm. In a specificexample, a 350 μm by 350 μm LED unit operating at 3.0 V and 0.02 A mayproduce about 8 lm. Each light engine provides the required amount oflight for a particular application. The amount of light is varied bychanging the number of LED units, rather than changing the current drivein the LEDs, as is done in conventional LED lamps. If it is desired forthe light engine to produce 1000 lm, then about 125 LED units may berequired in the light engine. The luminous efficacy of such an array maybe calculated by multiplying the voltage and current of each LED unittogether, then multiplying by the number of LED units and dividing thisinto the total lumen output (light output per LED unit times the numberof light units) for the light engine. In this example, the luminousefficacy of the light engine of the present invention is about 135 lm/W.

FIG. 10 is a schematic showing several examples of electricalconfigurations of arrays of relatively small LEDs operating atrelatively low current and near peak luminous efficacy. For example, insome embodiments of the present invention, the individual LED units maybe electrically coupled in parallel as shown in FIG. 10B, in series asshown in FIG. 10C or a combination of series and parallel connections asshown in FIGS. 10A and 10D. In some embodiments, a portion or all of theindividual LED units may be coupled anode to cathode as shown in FIGS.10A to 10D while in other embodiments parallel LEDs or parallel stringsof LEDs may be electrically couples such that one or more anode and oneor more cathode are electrically coupled at the end or ends of theseries strings, as shown, for example, in FIG. 10E, and in otherembodiments, a combination of these types of couplings may be utilized.The configuration shown in FIG. 10E and ones similar to it may be usedto operate the LED array on AC power. Individual LED units operate on DCpower, but using a configuration like the one shown in FIG. 10E maypermit AC operation as follows; during the positive half of the AC cyclethe LED units that are positively biased turn on and emit light whilethe LED units that are reverse biased turn off and block the flow ofcurrent. When the AC cycle reverses, the LED units that were previouslyon now turn off and the ones that were previously off now turn on. FIG.10E shows one configuration that may be used for AC powering of the LEDarray, however this is not a limitation of the present invention and inother embodiments, other AC configurations may be used.

As was discussed in the Background of the Invention section, operationof conventional LEDs in their normal operating range results in arelatively lower luminous efficacy. For example, a Cree XP-E white LEDmay produce about 122 lumens when operated at about 3.5 volts and acurrent of about 0.5 A. Production of about 1000 lm would require 9 ofthese Cree XP-E lamps and the luminous efficacy would be about 70 lm/W,about half of that for the present invention. In another example, aLuminus Devices SST-90 white LED may produce about 700 lm when operatedat about 3.1V and about 3.2 A. Two of these would be required to produceabout 1000 lm (actual light output would be 1400 lm) with a luminousefficacy of about 70 lm/W. As has been discussed, the luminous efficacyvalues in actual operation may be less because of the high temperaturesgenerated when operated in the normal operational range. For example, inthe case of the Cree XP-E lamp, a maximum junction temperature of 70° C.would require the light output be derated to about 88% of its roomtemperature value. This would result in ten lamps being required for the1000 lm light engine and a luminous efficacy of about 62 lm/W. In thecomparison of the Cree XP-E lamps and the present invention, each systemproduces that same optical power, about 1000 lm, or about 3.3 watts ofoptical power. However, because of the large difference in luminousefficacy, the Cree system generates about 14 watts of heat while that ofthe present invention generates about 3 to about 6 watts.

The relatively much smaller heat generation in some embodiments of thepresent invention has a large number of benefits. These include a lowerjunction temperature, longer operating time, reduced thermal managementrequirements and cost, reduced color shift and simplified design,relaxed requirement for thermally stable phosphors and higherefficiency. Based on the higher luminous efficacy achieved in thepresent invention the junction temperature of the LED units in someembodiments of the present invention may be less than 75° C., or lessthan 65° C., or less than 55° C. As was discussed with reference to FIG.2, lower junction temperatures translate to longer lifetimes. Lower heatlevels may lead to simplified requirements for the thermal managementsystem, heatsinking, etc. as well as reduced costs of these and relatedcomponents.

Another aspect of heat management is related to the fact that all LEDsshift their output color with changes in temperature. These shifts aretypically worse for AlInGaP materials than for nitride-based materials,but color shifts that may be visible to the human eye may occur in allLED materials. One cause of this type of color shift is an increase inthe current or current density to change the light intensity. As the LEDheats up the color shifts. This is in particular a problem in colormixing systems, for example when using red, green and blue LEDs,phosphor converted white LEDs and red LEDs or color mixing in phosphorconverted systems. By operating at higher luminous efficacies, less heatis generated and thus less color shift occurs. Some conventional LEDlamp or lighting systems employ sensors to detect the color andcorrection circuitry to change the intensity of various light emittingelements of the system to achieve a constant color output. Such a systemmay not be necessary using the light emitting device of the presentinvention. In addition to the color shift of directly emitted light fromLEDs as a function of temperature, phosphor (or light other lightconversion material) efficiency may also be a function of temperatureand thus as the temperature increases the phosphor efficiency maydecrease. The spectral characteristics of the phosphor may also changeas a function of temperature. Thus in any systems comprising a phosphoror other light conversion material, color shifts may additionally occurfrom changes in the phosphor efficiency, changes in the phosphorspectral characteristics and/or changes in the combination of the lightemitted directly by the LED and the phosphor (or other light conversionmaterial).

In a first embodiment of this aspect of the present invention theplurality of LED units may comprise a plurality of packaged LEDs. Insome embodiments of this aspect, the packaged LEDs may be mounted overor on a carrier, circuit board, a metal core circuit board or the like.The carrier may comprise portions for mounting of each packaged LED aswell as conductive elements which may electrically couple the anode andcathode of each LED package to anodes and/or cathodes of other LEDpackages.

Some embodiments of this aspect of the present invention may also employa light sensor that communicates with the driver or electronics to makerelatively small adjustments to the power input (for example currentinput) to the LED array to ensure a relatively narrow distribution inthe total luminous intensity from LED array to LED array or lamp tolamp. For example, in an LED array designed to provide about 1000 lm,some arrays may produce about 950 lm and some may produce about 1050 lm.In the former case the electronics may increase the input power toprovide a luminous flux of about 1000 lm, while in the latter case theelectronics may decrease the input power to provide a luminous flux ofabout 1000 lm.

The conventional LEDs (or LED packages) discussed above are comprised ofa LED die in a package. The LED die and packages used in conventionalLED lamps are designed to support high current and high temperatureoperation and thus are relatively expensive. The price for the Cree XP-Elamp in quantities of 1000 is about $4.40 each and thus the price forthe LEDs alone (not counting a carrier or assembly costs) for such anarray or light engine would be relatively expensive. For example, anarray having 100 LEDs would have a cost of just the LEDs of about $440.Thus while such a light emitting device would have a relatively highluminous efficacy, its relatively high cost may not be acceptable inmost applications.

In another aspect of this embodiment of the present invention, thepackaged LEDs may comprise a relatively small LED die in a relativelyinexpensive package. Such an aspect may have more packaged LEDs perlight engine than in the previous example because in this case, each LEDmay emit less light than in the preceding example. In one example theLED package may comprise a surface mount package. In this embodiment itis important that the cost of the die and the package, as well as themeans of mounting the packaged LEDs onto the carrier, circuit board,metal core circuit board or the like, be as inexpensive as possible.

In a second aspect of this embodiment of the present invention, theplurality of LED units may comprise a plurality of unpackaged LED die.In some embodiments of this aspect, the LED die may be mounted over acarrier, for example a circuit board, a metal core circuit board, asemiconductor wafer or other support structures. For example the LED diemay be mounted over a carrier comprising silicon, aluminum nitride,silicon carbide, diamond, sapphire or other materials. The carrier maycomprise portions for mounting of each packaged LED as well asconductive elements which may electrically couple the anode and cathodeof each LED package to anodes and/or cathodes of other LED packages. Insome embodiments it may be desirable for the carrier to have a highthermal conductivity.

In some embodiments of this aspect of the present invention, the LED diemay be mounted over an electrically conductive carrier while in otherembodiments the LED die may be mounted over a carrier that iselectrically insulating. For example, a conductive carrier may comprisea metal such as aluminum or copper, silicon, conductive aluminum nitrideor conductive silicon carbide. An insulating carrier may comprise, forexample, glass, sapphire, insulating aluminum nitride or insulatingsilicon carbide. In some examples the carrier may be electricallyconductive, with an electrically insulating film or material formed overall of or portions of the carrier and in some cases further electricallyconductive elements may be formed over portions of or all of theelectrically insulating film or material. In other examples the carriermay be electrically insulating, and electrically conductive elements maybe formed over portions or all of the electrically insulating carrier.

FIG. 11 is a schematic of one embodiment of this aspect of the presentinvention comprising a plurality of LED die 1052 formed over carrier1050. LED die 1052 comprise a semiconductor chip, a bottom contact (notshown) and a top contact 1054. Carrier 1050 may comprise an electricallyinsulating material, for example silicon carbide, aluminum nitride,sapphire or silicon with a layer of silicon dioxide formed over it.First conductive elements 1056 may be formed over carrier 1050 and thebottom contact of LED die 1052 may be electrically coupled to firstconductive elements 1056. In some embodiments LED die 1052 may beattached to first conductive elements 1056, for example using a solderor conductive epoxy or adhesive. In this example there are five parallelstrings of LED die 1052, with each string comprising five LED die 1052electrically coupled in series. However, this is not a limitation of thepresent invention and in other embodiments number of LED die 1052 andother series and parallel couplings may be utilized. The seriesconnection is made by electrically coupling the bottom contact (notshown) of one LED 1052 to top contact 1054 of the adjacent LED die 1052in the series string using a bonding wire 1058. Second conductiveelement 1060 and third conductive element 1062 may form contact areasthrough which electrical connection to the LED array is made.

In the example shown in FIG. 11 LED die 1052 are in part electricallycoupled using bond wires 1058. In one example bond wires 1058 maycomprise gold bond wires. However, this is not a limitation of thepresent invention and in other embodiments LED die 1052 may beelectrically coupled using other coupling elements, for example usingair bridges, evaporated conductive elements, buss bars, or other suchcoupling elements or combinations of such coupling elements.

In the example shown in FIG. 11, carrier 1050 is insulating. Howeverthis is not a limitation of the present invention and in otherembodiments carrier 1050 may be electrically conductive.

In the example shown in FIG. 11, LED die 1052 are shown as cube shapedwith a top and bottom contact. However this is not a limitation of thepresent invention and in other embodiments LED die 1052 may have anyshape and may have contacts in any orientation, for example LED die 1052may have two contacts on one side of the die.

In FIG. 11, LED die 1052 are shown in a regular periodic array, howeverthis is not a limitation of the present invention and in otherembodiments other configurations may be utilized.

LED die 1052 may be attached to carrier 1050 using, for example, solder,glue or adhesive. An example of a solder is an alloy of gold and tin.Adhesives may be electrically conductive, thermally conductive or both.In some embodiments of this aspect of the present invention the die maybe mounted on or over carrier 1050 using a thermally and electricallyconductive adhesive. In other examples LED die 1052 may be mounted overor on carrier 1050 using bonding techniques, for examplethermocompression bonding. However this is not a limitation of thepresent invention and in other embodiments LED die 1052 may be mountedover or attached to carrier 1050 by any technique and with anyattachment materials.

In some embodiments of this aspect of the present invention, one or moreportions or all of carrier 1052 may be reflective to a wavelength oflight emitted by LED die 1052. Such reflectivity may be achieved bychoice of the material comprising carrier 1050 or by the application ofa reflective coating over all of or portions of carrier 1052. Forexample a reflective coating may comprise silver, gold aluminum or thelike. In some embodiments of this aspect of the present invention, thereflective coating may comprise a plurality of layers. In other examplesthe reflectivity may be achieved using a Bragg reflector.

FIG. 12 is a schematic of another embodiment of this aspect of thepresent invention comprising a plurality of depressions 1070 in carrier1050 into which one or more LED die 1052 may be positioned. Carrier 1050may comprise an electrically insulating material, for example siliconcarbide, aluminum nitride, sapphire of silicon with a layer of silicondioxide formed over it. In some embodiments of this aspect of thepresent invention, a conductive element 1056 may be formed over aportion of or all of the surfaces of depression 1070 as well as aportion of or all of the surface of carrier 1050 The bottom contact (notshown) of LED die 1052 may be electrically coupled to first conductiveelement 1056. In some embodiments LED die 1052 may be attached to firstconductive element 1056, for example using a solder or conductive epoxyor adhesive. In this example there are five parallel strings of LED die1052, with each string comprising five LED die 1052 electrically coupledin series. The series connection is made by electrically coupling thebottom contact (not shown) of one LED 1052 to top contact 1054 of theadjacent LED die 1052 in the series string using bonding wire 1058.However, this is not a limitation of the present invention and in otherembodiments other number of LED die 1052 and other series and parallelcouplings may be utilized. Second conductive element 1060 and thirdconductive element 1062 may form contact areas through which electricalconnection to the LED array is made.

In the example shown in FIG. 12 LED die 1052 are in part electricallycoupled using bond wires 1058. In one example bond wires 1058 maycomprise gold bond wires. However, this is not a limitation of thepresent invention and in other embodiments LED die 1052 may beelectrically coupled using other coupling elements, for example usingair bridges, evaporated conductive elements, buss bars, or other suchcoupling elements or combinations of such coupling elements.

In the example shown in FIG. 12, carrier 1050 is insulating. Howeverthis is not a limitation of the present invention and in otherembodiments carrier 1050 may be electrically conductive.

In the example shown in FIG. 12, LED die 1052 are shown as cube shapedwith a top and bottom contact. However this is not a limitation of thepresent invention and in other embodiments LED die 1052 may have anyshape and may have contacts in any orientation, for example LED die 1052may have two contacts on one side of the die.

LED die 1052 may be attached to carrier 1050 using, for example, solder,glue or adhesive. An example of a solder is an alloy of gold and tin.Adhesives may be electrically conductive, thermally conductive or both.In some embodiments of this aspect of the present invention the die maybe mounted on or over carrier 1050 using a thermally and electricallyconductive adhesive. In other examples LED die 1052 may be mounted overor on carrier 1050 using bonding techniques, for examplethermocompression bonding. However this is not a limitation of thepresent invention and in other embodiments LED die 1052 may be mountedover or attached to carrier 1050 by any technique and with anyattachment materials.

In some embodiments of this aspect of the present invention, one or moreportions or all of carrier 1052 and/or a portion or all of depressions1070 may be reflective to a wavelength of light emitted by LED die 1052.Such reflectivity may be achieved by choice of the material comprisingcarrier 1050 or by the application of a reflective coating over all ofor a portion of carrier 1052. For example a reflective coating maycomprise silver, gold aluminum or the like. In some embodiments of thisaspect of the present invention, the reflective coating may comprise aplurality of layers. In other examples the reflectivity may be achievedusing a Bragg reflector.

Depressions 1070 may have surfaces positioned such that light exitingfrom a portion or of LED die 1052 is reflected in a directionperpendicular to or substantially perpendicular to the surface 1062 ofcarrier 1050. For example, light emitted from the sides of LED die 1052may be reflected in a direction perpendicular or substantiallyperpendicular to the surface 1062 of carrier 1050. In other embodiments,the surfaces of depressions 1070 may be oriented to reflect light in aparticular direction.

In the example shown in FIG. 12, one LED die 1052 is positioned in eachdepression 1070. However, this is not a limitation of the presentinvention and in other embodiments, two or more LED die 1052 may bepositioned in each depression 1070 and in some embodiments one or moredepressions 1070 may not contain any LED die 1052. In FIG. 12,depressions 1070 are shown in a regular periodic array, however this isnot a limitation of the present invention and in other embodiments otherconfigurations may be utilized.

In the example shown in FIG. 12, the orientation of all of the surfacesof each depression is the same. However, this is not a limitation of thepresent invention and in other embodiments carrier 1050 may comprisesub-arrays of depressions, with each sub-array of depressions havingdifferent surface orientations. In one example the surface orientationsof the plurality of sub-arrays of depressions may be oriented to achievea wide spread of light from the LED array. In another example thesurface orientations of the plurality of sub-arrays of depressions maybe oriented to achieve a narrow spread of light from the LED array.However, this is not a limitation of the present invention and in otherembodiments the LED array may comprise any number of sub-arrays ofdepressions with different surface orientations to achieve any arbitrarylight distribution.

In the example shown in FIG. 12 the bottom surface (not shown) ofdepressions 1070 may be parallel or substantially parallel to surface1062 of carrier 1050. However, this is not a limitation of the presentinvention and in other embodiments the bottom surface (not shown) ofdepressions 1070 may have any orientation relative to surface 1062 ofcarrier 1050 and in some embodiments, carrier 1050 may comprisesub-arrays of depressions, with each sub-array of depressions havingbottom surface (not shown) orientations different from each other.

In FIG. 12 LED die 1052 are shown as being positioned within depressions1070. However this is not a limitation of the present invention and inother embodiments depression 1070 may comprise a platform, a slopedplatform or other means for positioning and orienting LED die 1052.

In FIG. 12, depression 1070 are shown as having a square cross section,however this is not a limitation of the present invention and in otherembodiments, depression 1070 may be circular, hexagonal, triangular orany arbitrary shape. In FIG. 12, all depressions 1070 are shown ashaving the same shape, however this is not a limitation of the presentinvention and in other embodiments a first portion of depressions 1070may have a first shape and a second portion of depressions 1070 may havea second shape.

Some embodiments of this aspect of the present invention may comprise anoptional light conversion material (not shown in FIG. 11 or 12), forexample an organic or inorganic phosphor or other material capable ofabsorption of a portion of the light emitted from LED die 1052 andre-emitting it at a different wavelength. In some embodiments of thepresent invention the light conversion material may comprise a downconversion material and in other embodiments light conversion materialmay comprise an up conversion material. In some embodiments of thepresent invention, the light conversion material may be suspended orembedded in a second material (not shown), and in some embodiments thesecond material may comprise a material with an index of refractionbetween that of the semiconductor material in LED die 1052 and air. Inone example of this embodiment such second material may comprise forexample an epoxy, gel, or resin with an index of refraction in the rangeof about 1.2 to about 1.7. Such a second material may act to reducetotal internal reflection and increase the light extraction efficiencyof the light engine. The light conversion material may be formed overall or a portion of LED die 1052 in the light engine. The lightconversion material may be deposited by spinning, screen printing, inkjet printing, dispensing or the like; the method of deposition is not alimitation of the present invention. Some embodiments of this aspect ofthe present invention comprising recesses in the substrate, asexemplified in FIG. 12 may comprise a light conversion material thatpartially or completely or substantially completely covers or fills theremaining volume within the recesses. In some embodiments, all of therecesses may be covered or filled or partially covered or filled with alight conversion material but this is not a limitation of the presentinvention and in other embodiments, only a portion or none of therecesses may be covered or filled with a light conversion material.

In some embodiments of this aspect of the present invention, LED die1052 may comprise a first portion of LED die 1052 and a second portionof LED die 1052, wherein said first and second portions of LED die 1052may have different properties, for example they may emit with adifferent color.

In some embodiments of this aspect of the present invention, assemblymay comprise assembly using conventional semiconductor packaging tools,for example tools that may automatically pick and place die at theproper location. However this is not a limitation of the presentinvention and in other embodiments other assembly techniques may beutilized. For example another assembly technique may comprise a keyedsystem wherein the individual die and their desired locations are keyedto attract each other, for example using electric charge, magnets,shapes, etc. Another example of an assembly technique may be fluidicassembly. In some embodiments of this aspect of the present inventionwherein LED die 1052 may comprise a first portion of LED die 1052 and asecond portion of LED die 1052, and wherein said first and secondportions of LED die 1052 may have different properties, said firstportion of LED die 1052 may be keyed differently than said secondportion of LED die 1052, permitting controlled assembly of first andsecond portions of LED die 1052 in specific locations on carrier 1050 orin specific depressions 1070.

Some embodiments of this aspect of the present invention may comprise alight sensor that communicates with the electronics to make relativelysmall adjustments to the power input to the LED array to ensure arelatively narrow distribution in the total luminous intensity from LEDarray to LED array or lamp to lamp. For example, in an LED arraydesigned to provide about 1000 lm, some arrays may produce about 950 lmand some may produce about 1050 lm. In the former case the electronicsmay increase the input power to provide a luminous flux of about 1000lm, while in the latter case the electronics may decrease the inputpower to provide a luminous flux of about 1000 lm.

In a third aspect of this embodiment of the present invention, theplurality of LED units may comprise an array of LED units fabricatedmonolithically on a common substrate using batch semiconductorprocesses. At the end of the process, the substrate is separated intocomplete light engines. Each light engine provides the required amountof light for a particular application. The amount of light is varied bychanging the number of LED units in the light engine at the design andmanufacturing stage, rather than changing the current drive in the LEDs,as is done in conventional LED lamps. This batch processing approachresults in the light engine of this aspect of the present inventioncosting relatively significantly less than a comparable light engineusing conventional LEDs or LED die mounted on a carrier, as discussedabove or a conventional LED lamp using individual packaged LEDs.

The lower cost of this aspect of the present invention comes fromseveral factors. Conventional packaged LEDs are fabricated by firstdepositing a plurality of films forming the LED structure on asubstrate. The LED is then fabricated, generally including formingelectrical contacts to the p- and n-layers of the LED. Other processesmay also take place, for example to improve current spreading or lightextraction. The substrate is then singulated to form individual LED die,after which the LED die are placed into packages. It is to be understoodthat the foregoing explanation is a general one for purposes ofdescription, and is not meant to represent the actual process used whenmaking LED die or packaged LEDs.

In an embodiment of this aspect of the present invention, the steps asdescribed above for prior art LED die are generally the same up to theon-wafer fabrication steps. However, in an embodiment of this aspect ofthe present invention the processing at the wafer level continues tofabricate the light engine, as will be described below, resulting in aplurality of complete light engines on each wafer at the completion ofwafer processing. The wafer is then singulated, resulting in severalhundred light engines, of which only one may be required for each lamp.Thus all of the “taking apart and putting back together” steps in theconventional LED lamp approach, for example including singulation ofindividual LED die, packaging of individual LED die, fabrication of thecarrier or circuit board and mounting of the LED packages on the carrieror circuit board are eliminated, saving parts cost, assembly cost andassembly time.

Large diameter wafers permit fabrication of many light engines on awafer. In the example given above for the present invention, using asquare LED unit with a side dimension of about 350 μm and a spacingbetween LED units of about 50 μm, results in about 200 light engines ona 100 mm diameter substrate. Use of larger diameter wafers increases thenumber of light engines per wafer. As is the case with electronicintegrated circuits, increasing the wafer diameter may result in afurther reduction in the cost of each light engine. Using a 100 mmdiameter wafer, the cost of the light engine of an embodiment of thisaspect of the present invention may be able to be fabricated for about$5.00 or less. In comparison, conventional packaged high power LEDs costin the range of about $2 to about $5 each, and thus a prior-art LED lamphaving 10 such LEDs would have a cost of about $20 to about $50 just forthe packaged LEDs. This does not include the cost of assembly or anyother lamp parts. Thus the cost of the entire light engine of anembodiment of this aspect of the present invention (capable, forexample, of outputting about 1000 lm) may be similar to the price of acouple packaged LEDs. However such a light engine may have a higherluminous efficacy as described herein.

The light engine of an embodiment of this aspect of the presentinvention may use about 2-3× more wafer area than the combined waferarea in conventional packaged LEDs for a similar light output. However,this cost occurs at the wafer level, which may be significantly lessexpensive than the cost of using packaged LEDs. A further cost savingscomes from the fact that the light engine of the present invention iscomplete after singulation from the wafer, whereas in the prior artdevices the individual LEDs have to be mounted and connected together ona carrier.

In prior art light emitting devices the packaged LEDs may be binned byluminous intensity, forward voltage and color by the manufacturer. Inother words, every LED may have to be tested and then separated intogroups or bins of like characteristics. Typically LEDs with relativelymore desirable characteristics, for example a higher luminous intensity,have a higher price. Binning may be required because the manufacturingprocess does not have a suitably tight distribution and thus LEDs with arange of characteristics are produced on each wafer, from wafer towafer, growth run to growth run, from fabrication run to fabrication runand from packaging run to packaging run. In addition to complicating themanufacture and use of such LEDs, binning adds to the cost of each LED.

LEDs are typically binned by peak wavelength, forward voltage andluminous intensity. This presents a problem for lamp manufacturers whouse a plurality of these LEDs in a lamp to achieve a desired lightoutput. When combining separately packaged LEDs, control and uniformityof the I-V characteristics becomes important, especially when LEDs areconnected in parallel. In a parallel configuration with LEDs withwell-matched I-V characteristics, each LED will draw substantially itsequal share of the total current. For example if four LEDs areelectrically coupled in parallel, then each LED, when their I-Vcharacteristics are well matched, will draw about ¼ of the totalcurrent. However, if the I-V characteristics of the LEDs are not wellmatched, the LED with the lower turn on voltage will draw adisproportionately large share of the total current, emit relativelymore light and have a relatively higher junction temperature. In thisscenario the lifetime of the different LEDs may be different because ofthe relatively large current and junction temperature mismatch betweenthem. Light uniformity also becomes an issue in this case, as the lampuses only a relatively small number (10-20) of high-power LEDs. If thelight output of a small percentage of the LEDs is relativelysignificantly different from the others, it is difficult to homogenizethe light, resulting in a lamp with relatively dim and bright (hot)spots.

This effect becomes relatively more important at higher drive currents,where the I-V characteristics are relatively linear. In the LEDdiscussed in reference to FIG. 3, if the difference in the I-Vcharacteristics between two LEDs electrically coupled in parallel isabout 5%, then the lower turn on voltage LED may have about a 25% highercurrent at a low operating voltage of about 2.5 V, compared to about a38% higher current at a relatively high operating voltage of about 3.5V.

Because individual packaged LEDs have variability in their intensity(luminous efficacy), color and I-V characteristics, the LEDmanufacturers have to bin the LEDs, that is test and separate them intoa number of categories, for use by lamp or luminaire manufacturers. Thisleads to a lower yield of packaged LEDs that meet the lampmanufacturer's specifications and thus higher costs. For example, atypical LED process may have 8 color bins, 3 flux bins and 4 forwardvoltage bins. If the a customer desires to specify a portion of the LEDsfrom each category, for example they will take 30% of the availablecolor bins, 55% of the available flux bins and 70% of the availableforward voltage bins, the best yield for this choice is only about 11%of the full distribution. Such a low yield is not commerciallyacceptable, and thus at this point in time, manufacturers are typicallylimited to selecting portions of only one, or perhaps two of the 3 bins.For example if a manufacturer prioritizes on color and acceptsvariations in forward voltage or flux, or a manufacturer prioritizes onflux and accepts variations in color and forward voltage, the expectedyield from these selections increases to about 70% to about 80% of thefull distribution (Jeffrey Perkins, Yole Development, “LED ManufacturingTechnologies and Costs,” DOE SSL Workshop, Fairfax, Va. April 2009).Thus, in the prior art approach, while the yield has increased, this isat the expense of the ability to specify all three characteristics ofthe packaged LEDs comprising the LED lamp.

Another aspect of the present invention related to reduction of costsassociated with binning is the fact that less testing and sorting isrequired in some embodiments of the present invention. In someembodiments of the present invention, the light engine, comprising thearray of LED units, may be tested instead of testing each LED unitindividually. This results in a reduction in the number of devices to betested by a factor of about 20 to about 100.

In this embodiment of this aspect of the present invention the binningissue is addressed in three ways. First, all of the LED units in eacharray are fabricated at the same time from one epitaxial structure,minimizing epitaxial structure and fabrication-related differences.Second, on-wafer variations in each LED array are minimized because theLED array may cover only a relatively small portion of the area of theentire wafer, for example and area of about 5 mm by about 5 mm, or lessthan about 0.5 cm2 or less than about 0.25 cm2 and over this small anarea the properties of the epitaxial structure and the fabricationprocess are relatively very uniform. Third, the LED units are driven atrelatively low currents or in the part of I-V curve in which the changein current resulting from a given voltage change is relatively smallerthan at high currents. Thus the forward voltage, light output and colorvariations for the LED units within each light engine are relativelymuch less than those from packaged LEDs, which may have come fromdifferent wafers, runs or manufacturing lots produced over a wide rangeof times. From a lamp perspective, the present invention eliminatesforward voltage binning, because only one light engine is used per lamp.

In order to achieve widespread acceptance a light engine or light systemmust have an acceptably low first or purchase cost, and must have a lowtotal cost of ownership. Conventional incandescent and fluorescent lampshave a relatively low first cost (in the range of about $0.60 to about$10). However, their total cost of ownership is relatively high becauseof their low luminous efficacy. Prior art LED lamps have a relativelymuch higher first cost (in the range of about $50 to about $125). Soeven though they have a relatively lower total cost of ownership, theiracceptance is low because of the long payback time.

A light engine of the present invention, utilizing a monolithicallyfabricated array of LED units operating at near peak efficiency may costrelatively significantly less to operate than both prior art LED systemsand conventional lighting systems. FIG. 13 shows a graph showing theoperating cost of a kilolumen (1000 lm) of light per year as a functionof the operating time per week for a variety of lighting systemsincluding an A19 incandescent lamp (1200 lumen, 100 watt lamp, $0.60), aPAR30 incandescent lamp (1000 lumen, 75 watt, $4.99), a CFL PAR-typelamp (640 lm, 12 watt, $3.50), a state of the art prior art LED lamp(Cree LR-6, 650 lm, 12 watt, $100), a state of the art T8 electronicballast fluorescent lamp (14.3 watts, 1000 lm, $4.00) and a lamp usingthe light engine of the present invention (1000 lm, 10 watts, $20.00).At the low end of the scale, an operating time of about 14 hours perweek represents an approximate average operating time in residentialusage. On the high end, 168 hours represents continuous operation.

FIG. 14 shows the payback time in years and electricity cost as afunction of lamp operation time per week for a LED lamp using amonolithically fabricated light engine of the present invention comparedto a conventional LED lamp. In residential use the payback time is about1.4 years, which is about 7 times faster than state-of-the-artconventional LED lamps. Since an incandescent lamp in residential usehas a lifetime of about 1.5 years, the 1.4 year payback time issubstantially equivalent to one incandescent bulb lifetime.

The payback time calculation in the preceding paragraph is referenced toa PAR 30 incandescent lamp (1000 lm, $5 first or purchase cost and alifetime of 1000 hr). The electricity cost is assumed to be about14.7¢/kWh which is that for the state of CA. The payback time used hereis an out-of-pocket payback time; it occurs when the cost of the LEDlamp plus its electricity cost equals the cost of the incandescent lampplus its electricity cost. This calculation includes the purchase of anadditional incandescent lamp at the end of the payback time, to reflectthe fact that going forward one would need a new lamp. This may be amore realistic and real-world calculation than one based on amortizationof the LED lamp cost over its entire lifetime.

Another aspect of the present invention relates to the impact of thenumber of LED units within the array. An alternate configuration may beto use only one large LED unit operating at relatively low currentdensity to achieve high luminous efficacy. However, there are severaladvantages over this approach that arise from the use of a larger arrayof smaller LED units.

First, one or a few very large LED units may have a lower luminousefficacy because of a reduced light extraction efficiency associatedwith a very large die. Light is guided within the epitaxial structurelaterally and multiple small LEDs have a large number of edges to aid inbreaking these modes and causing the light to exit the LED die. In avery large die, these edges do not exist and light may be trapped withinthe epitaxial structure for a much longer distance, resulting in moreabsorption, less emitted light and a lower luminous efficacy.

Second, one or a few very large LED units may have a lower yield thanthe yield of light engines comprised of a relatively large array ofrelatively small LED units. If a killer defect (one that prevents properdevice operation, for example either making the LED non-operational ornot meeting specifications) occurs in a light engine with one large LEDunit, that LED unit is dead and so is the entire light engine. With arelatively large number of relatively small LED units, the same killerdefect may prevent operation of one LED unit in the light engine butthis will still permit operation of the light engine.

There are two significant kinds of killer defects; one that results in ashorted LED and one that results in an open LED. For LEDs in series orparallel, the shorted LED defect has the least impact, resulting in oneless operational LED. The open LED defect has a larger impact on stringsof LEDs in series; if one LED in a string is open, then no current canflow to any LEDs in that string. In spite of these differences, theimpact of either of these types of killer defects is relativelysignificantly larger for a small number of LEDs.

For example, if one LED unit in a light engine having 11 parallelstrings of 11 LED units in series (121 total LED units) is notfunctional, then that one entire string of 11 LED units may notfunction. However, the current will divide up equally in the remaining10 parallel strings, resulting in a relatively small increase in currentin each LED unit. If each LED unit operates at 20 mA with a forwardvoltage of 2.9V and produces about 8.7 lm, then the total light outputwill decrease by only about 1.2% and the luminous efficacy of the lightengine will decrease by only about 1.7%. In another embodiment of thepresent invention, a sensor may be used to detect the total light outputand adjust the current to the remaining operating LEDs. In this case thetotal light output would remain the same and the luminous efficacy woulddecrease by about 1.9%. FIG. 15 is a graph showing the change inluminous efficacy and light output as a function of the number ofnon-operating strings of LEDs for this example (11×11 array of LEDunits). The dotted line shows the change in luminous efficacy as afunction of non-operating strings with no current adjustment to maintainthe same light output. The solid line shows the change in light outputas a function of non-operating strings with no current adjustment tomaintain the same light output. The dashed line shows the change inluminous efficacy as a function of non-operating strings when thecurrent is adjusted to maintain the same light output. Even with twonon-operating strings, the light output and luminous efficacy (with nocorrection) decrease by about 2.4% and 3.4% respectively. In contrast,with only one large LED unit, the entire light engine would benon-operational.

If the light engine comprised one or only a few relatively large LEDunits, the impact of one non-operational LED unit would be much moresignificant. For example, using the Luminus Devices LED data shown inFIGS. 1 and 3, two such LEDs operating at about 1.4 A each would produceabout 1000 lm with a luminous efficacy of about 118 lm/W. If one of theLEDs becomes non-operational, the current in the remaining LED wouldincrease to about 2.8 A, producing about 954 lm with a luminous efficacyof about 98 lm/W, about a 17% reduction in luminous efficacy and about a4.6% decrease in light output (lm). Note that these values, especiallythe reduction in luminous efficacy, are much larger than those of thepresent invention. One may expect a further decrease in the luminousefficacy of the LED lamp in which these LEDs are used, because more heatis generated, resulting in a decrease in ηThermal.

This argument may also be applied to conventional LED lamps usingpackaged LEDs. In a prior-art LED lamp, the lamp comprises a relativelysmall number of high brightness LEDs. For example, a prior-art LED lampmay comprise about 12 to about 20 high brightness LEDs. Thus each LED inthe lamp emits about 8.3% to about 5% of the total light output of thelamp. If one or more lamps fail, this will reduce the light output andmay adversely affect other characteristics, for example luminousefficacy. For example, if all the LEDs in a conventional lamp areconnected in series and one fails by shorting, the total LED voltagedrops by about the value of the on-voltage of one LED. If two fail byshorting, the total LED voltage drops by about two times the value ofthe on-voltage of one LED. In this case the light output will decreaseby about 8.3% and about 16.6% respectively, and the electronics/driverefficiency may drop because the total LED voltage has decreased. If allof the LEDs are connected in series and one fails open, then currentcannot flow and the entire lamp has failed.

The reduction in luminous efficacy and light output for the presentinvention can be reduced further by changing the configuration of theLEDs units. Increasing the number of parallel strings while reducing thenumber of LED units in series causes the death of one LED string to haveless of an impact. For example, an array of 12 parallel strings of 10LED units in series would have a reduction of luminous efficacy andlight output of 1.5% and 1.1% respectively if one string becamenon-operational. The limiting case of this would be to have all of theLED units in parallel, however this may have an adverse impact on theoverall lamp luminous efficacy, as discussed below.

Third, one or a few large LED units may have a reduced electronics ordriver efficiency ηDriver. As was discussed with respect to FIG. 6,ηDriver is in part affected by the output voltage of the driver. If onlyone or a few very large LEDs are used in the LED lamp, the outputvoltage may be in the range of about 4 V to about 16V (for one to fourLEDs). This results in large difference between the input voltage 120Vand the output voltage, leading to a reduced ηDriver. Using therelatively large array of LED units of the present invention permits arelatively much higher output voltage, by putting more LED units inseries, resulting in an increased ηDriver.

However, as was discussed previously, putting more LED units in series,and thus having less parallel strings, increases the impact of one ormore non-operational LED units. Thus one approach may be to optimize theconfiguration to achieve the best efficiency and the least impact of anon-operational LED. In part this optimization will depend on the yieldstatistics from the manufacturing process.

Another approach to minimizing the impact of one or more non-operationalLED units is to provide cross connection between parallel strings ofLEDs as shown in FIG. 16. FIG. 16A shows one cross connection betweenall of the parallel strings of LED units, while FIG. 16B shows the mostcomplete version of cross connection, in which every LED unit is crossconnected. In the case corresponding to FIG. 16B, if one LED unit isnon-operational, the current in the remaining LED units in that row willincrease. In the example given above having 121 LED units, the currentin the row comprising the non-operational LED unit may increase by about10%. This may, for the light engine, result in an overall reduction inlight output of about 0.11% and a reduction in luminous efficacy ofabout 0.26% respectively for one non-operational LED unit. The advantageof this approach is that it permits independent optimization of theconfiguration of the LED array for optimum electronics efficiency whileachieving very low sensitivity to one or a few non-operational LEDunits.

Another aspect of an embodiment of the present invention is related tothe etendue (etendue refers to how “spread out” the light is in area andangle) of the light emitting device. In a given lamp or fixture design,one can only capture all of the light from the light source if theetendue of the light source is below a certain value (that value dependson the optical design of the lamp or fixture). In other words, thesmaller the etendue, or the more compact the light source, the easier itmay be to use the light in an optical system and to minimize opticallosses. In an embodiment of the present invention comprising arelatively compact light source, for example a monolithically fabricatedlight engine, the etendue of the light source may be relatively small,thus permitting easier, more efficient and more flexible use of suchlight source in lamps, fixtures and other lighting systems. For examplea monolithically fabricated light engine of the present invention mayhave a light emitting area on the order of about 5 mm by about 5 mmwhich is relatively smaller and has a relatively smaller etendue thanthe light emitting area of tens of LEDs spread out over tens ofcentimeters of area of a circuit board or carrier in a conventional LEDlamp.

Some embodiments of this aspect of the present invention may comprise alight sensor that communicates with the electronics driver to makerelatively small adjustments to the drive current to the LED array toensure a relatively narrow distribution in the total luminous intensityfrom light engine to light engine or lamp to lamp. For example, in anLED array designed to provide about 1000 lm, some light engines mayproduce about 950 lm and some may produce about 1050 lm. In the formercase the electronics may increase the input power to provide a luminousflux of about 1000 lm, while in the latter case the electronics maydecrease the input power to provide a luminous flux of about 1000 lm.

Accordingly several embodiments of a monolithically fabricated lightengine of the present invention are described in further detail.

FIG. 17 is a cross-sectional view of a semiconductor structure 100 inaccordance with an embodiment of the present invention. Thesemiconductor structure in FIG. 17 may be referred to as amonolithically formed light system or light engine. The monolithic lightengine shown schematically in FIG. 17 comprises a carrier 1510, aplurality of LED units 110, a layer 1410 and a layer 1520 used to attachLED units 110 to carrier 1510, a filler material 1310, an optional lightconversion material 1810, a layer 1210, a contact region 120A and acontact region 120B. Carrier 1510 may be referred to as a carrier, asubstrate, a mechanical support, a heat sink or a first level heat sink.Layers 1410 and 1520 may be used to help attach LED units 110 to carrier1510. LED units 110 may comprise a bottom confining region 220, anactive region 230, a top confining region 240, a portion of layer 640, abottom electrical contact 910, a top electrical contact 1010, a portionof interconnect layer 1110, a portion of filler material 1310 and aportion of layer 1210. Layer 1210 may be used to electrically isolateLED units from each other and from layers 1410, 1520 and carrier 1510.

FIG. 18 is a view of the structure of FIG. 17 from the side of carrier1510 opposite that of LED unit 110 in accordance with an embodiment ofthe present invention and FIG. 17 is a cross-sectional view taken alongsection line 17-17 of FIG. 18. In FIG. 18 carrier 1510, attachmentlayers 1520 and 1410, filler material 1310 and layer 1210 are not shownfor clarity purposes. FIG. 19 is a view of the structure of FIG. 17 fromthe light emitting side, assuming for clarity purposes that lightconversion material 1810 is transparent.

Light is generated in active region 230 and exits LED unit 110 throughsurface 140 of bottom confining region 220, optional light conversionmaterial 1810 and its surface 130. In some embodiments of the presentinvention light extraction features may be formed in or over surface 140and/or surface 130 to improve the light extraction efficiency. In someembodiments of the present invention, light extraction features maycomprise one or more anti-reflection coatings and/or surface roughening,texturing, patterning, imprinting or the like. In some examples suchlight extraction features may be formed in a regular periodic array,however this is not a limitation of the present invention and in otherembodiments, light extraction features may be formed in a random orsemi-random pattern. In some embodiments of the present invention lightextraction features may be formed in or on the surface of substrate 210(FIG. 20) on which layer structure 250 (FIG. 20) is to be formed, priorto formation of layer structure 250 (FIG. 20) or at the interface ofsubstrate 210 (FIG. 20) and layer structure 250 (FIG. 20) or withinlayer structure 250 (FIG. 20) adjacent to substrate 210 (FIG. 20).

Some of the light generated in active region 230 may exit the activeregion into top confining region 240. Such light may be reflected fromreflecting surfaces that reflect a wavelength of light emitted by theLED that are formed over portions of or all of top confining region 240.In some embodiments of the present invention reflecting surfaces mayalso be formed over portions of or all of active region 230 and bottomconfining region 220. In some embodiments of the present invention, suchreflecting surfaces may have a reflectivity greater than 80% to awavelength of light emitted by the LED, or greater than 90% to awavelength of light emitted by the LED, or greater than 95% to awavelength of light emitted by the LED.

Optional light conversion material 1810 may comprise organic orinorganic phosphors or other materials capable of absorption of aportion or all of the light emitted from active region 230 andre-emitting it at a different wavelength. In some embodiments of thepresent invention light conversion material 1810 may comprise a downconversion material and in other embodiments light conversion material1810 may comprise an up conversion material. In some embodiments of thepresent invention, optional light conversion material 1810 may besuspended or embedded in a second material (not shown), and in someembodiments the second material may comprise a material with an index ofrefraction between that of the material in layer structure 250 (FIG. 20)and air. In one example of this embodiment such second material maycomprise for example an epoxy, gel, or resin with an index of refractionin the range of about 1.2 to about 1.7. Such a second material may actto reduce total internal reflection and increase the light extractionefficiency of the light engine.

LED units 110 are formed such that the heat-generating active regions230 may be in close proximity to carrier/heat sink 1510, for example allor a portion of active regions 230 may be spaced less than 10 μm, or maybe less than 5 μm, or may be less than 2 μm from the surface of carrier1510 adjacent to attachment layer 1520. In other words, the combinedthickness of attachment layer 1520, 1410, layer 1210, interconnect 1110,contact 1010 and top confining region 240 may be less than 10 μm, or maybe less than 5 μm, or may be less than 2 μm.

Referring now to FIG. 18, FIG. 18 shows an example of semiconductorstructure 100 comprising four (4) LED units 110. In FIG. 18 carrier1510, attachment layers 1520 and 1410, filler material 1310 and layer1210 are not shown, for clarity purposes, as discussed above. In thisexample the LED units 110 are configured as shown in FIG. 10A,comprising two parallel strings of LEDs, each string of LEDs comprisingtwo LED units 110. In this example electrical connection to the negativepolarity terminal of the light engine may be made through contact region120A, which comprises a portion of interconnect layer 1110 that may becoupled to bottom electrical contact 910A and 910B of LED units A and B.Similarly, electrical connection to the positive polarity terminal ofthe light engine may be made through contact region 120B, whichcomprises a portion of interconnect layer 1110 that may be coupled totop electrical contact 1010C and 1010D of LED units C and D. Topelectrical contacts 1010A and 1010B of LED units A and B respectivelymay be electrically coupled to bottom electrical contacts 810C and 810Dof LED units C and D respectively through interconnect layer 1110. Notethat in FIG. 18, all top electrical contacts 1010 and all bottomelectrical contacts 910 are shown as dashed lines to indicate that theyare underneath interconnect layer 1010.

FIG. 19 is a view of the structure of FIG. 18 from the light emittingside, assuming for clarity purposes that light conversion layer 1810 istransparent. The four LED units 110 (labeled A, B, C and D are visible,as are the contact regions 120A and 120B.

FIGS. 17 and 18 show an exemplary LED array with 4 LED units 110.However, the number of LED units 110 is not a limitation of the presentinvention and in some embodiments the LED array may comprise a largernumbers of LED units 110. In some embodiments of the present inventionthe number of LED units 110 in the array may be greater than 20, or maybe greater than 50, or may be greater than 100 or may be greater than250 or may be greater than 500.

FIG. 20 is a cross-sectional view of a semiconductor structure at abeginning stage of manufacture, in accordance with an embodiment of thepresent invention. FIG. 20 comprises substrate 210, bottom confiningregion 220 that may be formed over substrate 210, active region 230 thatmay be formed over bottom confining region 220 and top confining region240 that may be formed over active region 230. FIG. 20 may be used as astarting wafer for the fabrication of semiconductor structures of thepresent invention. Substrate 210 may comprise a semiconductor materialsuch as, for example, gallium arsenide (GaAs), gallium phosphide (GaP),indium phosphide (InP), sapphire, silicon carbide (SiC), aluminumnitride (AlN), ZnO, diamond, silicon or other semiconductors, and may bedoped or undoped depending on the application, although the methods andapparatuses described herein are not limited in this regard. In otherembodiments of the present invention, substrate 210 may comprise othermaterials such as, for example, glass, polymers or metals. Substrate 210may have a thickness ranging from about 50 μm to about 2,000 μm, butthis is not a limitation of the present invention and in otherembodiments the substrate may have any thickness. The thickness ofsubstrate 210 may be reduced through subsequent thinning processes insome embodiments. In some embodiments a portion or all of substrate 210may be ultimately removed from the final structure. In some embodimentssubstrate 210 may comprise more than one material, for example a layerof one material formed over a second material. In one example such asubstrate may comprise a zinc oxide layer (ZnO) layer formed over anon-crystalline substrate. Substrate 210 may be absorbing to orsubstantially transparent, or translucent at a wavelength of lightgenerated by the light-emitting device.

Substrate 210 may have a diameter in the range of about 1″ to more thanabout 12″, however the diameter of substrate 210 is not a limitation ofthe present invention and in other embodiments substrate 210 may haveany diameter. It may be desirable for substrate 210 to have a relativelylarge diameter, as this permits a larger number of LED arrays or lightengines to be fabricated in a batch mode on a single substrate (at thewafer level). In some embodiments of the present invention substrate 210may have a circular shape, like that often used for conventionalsemiconductor processing. However this is not a limitation of thepresent invention and in other embodiments substrate 210 may be square,rectangular or have any arbitrary shape.

In some embodiments bottom confining region 220 may be doped n-type andtop confining region 240 may be doped p-type, but this is not alimitation of the present invention and in other embodiments each layermay be either n-type, p-type or undoped. In some embodiments bottomconfining region 220 may have a thickness in the range of about 0.5 μmto about 10 μm. In some embodiments active region 230 may have athickness in the range of about 5 angstrom (Å) to about 10,000 Å. Insome embodiments top confining region 240 may have a thickness in therange of about 0.05 μm to about 5 μm. Together bottom confining region220, active region 230 and top confining region 240 may be referred toas layer structure 250. In some embodiments of the present invention LEDunit 110 may comprise a plurality of active regions 230 betweenconfining layers 220 and 240. In some embodiments of the presentinvention, these separate active regions may emit at the same ordifferent wavelengths.

In some embodiments of the present invention it may be desirable tominimize the thickness of layer structure 250. For example in someembodiments of the present invention, portions of layer structure 250may be removed, resulting in steps in layer structure 250 and minimizingthe thickness of layer structure 250 may simplify the processing steps,for example removal of portions of layer structure 250 and metallizationover said steps, by reducing said step or steps height.

The structure shown in FIG. 20 comprises the layer structure 250 formedover substrate 210 and may be referred to as an LED epi wafer. Bottomconfining region 220, top confining region 240 and/or active region 230may each comprise one or more layers. Bottom confining region 220 andtop confining region 240 may have a bandgap relatively larger than thatof all or a portion of active region 230 or of the one or more layerscomprising active region 230. In some embodiments of the presentinvention active region 230 may comprise one or more quantum wells andbarriers. In some embodiments of the present invention active region 230may comprise one or more layers of quantum dots, or quantum wires andbarriers. As is well understood by those familiar with the art,additional layers may be present and this invention is not limited inthis regard. Furthermore, the layers comprising layer structure 250 maybe comprised of a wide range of materials, depending on the desiredproperties, and in particular, the emission wavelength of the LED.

In some embodiments of the present invention top confining region 240may comprise a Distributed Bragg Reflector (DBR) (not shown) which mayact as a mirror to light of a wavelength emitted by active region 230.In some embodiments of the present invention the DBR (not shown) mayhave a reflectivity of higher than about 70%, or higher than about 80%,or higher than about 90% to light of a wavelength emitted by activeregion 230 perpendicularly incident upon said DBR. In other embodimentsof the present invention a DBR (not shown) may be formed over topconfining region 240 or between top confining region 240 and activeregion 230.

In some embodiments of the present invention layer structure 250 maycomprise epitaxial layers and be formed using techniques such as metalorganic vapor phase epitaxy (MOVPE), molecular beam epitaxy (MBE),hydride vapor phase epitaxy (HVPE), liquid phase epitaxy (LPE), chemicalvapor deposition (CVD) or the like. In some embodiments of the presentinvention layer structure 250 may comprise polycrystalline or amorphouslayers and be formed using techniques such as chemical vapor deposition(CVD), evaporation, sputtering or the like. However this is not alimitation of the present invention and in other embodiments layerstructure 250 may be formed by any means and may be single crystal,polycrystalline or amorphous.

In one example, in which the LED may emit red/orange/yellow light,substrate 210 may comprise GaAs, bottom confining region 220, activeregion 230 and top confining region 240 may comprise AlxInyGa1-x-yP,with x and y adjusted in each layer such that the bandgap of bottomconfining region 220 and top confining region 240 are larger than thebandgap of the light emitting layer in active region 230. In someembodiments of this example substrate 210 may be doped n-type, bottomconfining region 220 may be doped n-type and top confining region 240may be doped p-type.

In another example, in which the LED may emit UV, blue or green light,substrate 210 may comprise sapphire, bottom confining region 220, activeregion 230 and top confining region 240 may comprise AlxInyGa1-x-yN,with x and y adjusted in each layer such that the bandgap of bottomconfining region 220 and top confining region 240 are larger than thebandgap of the light emitting layer in active region 230. In someembodiments of this example substrate 210 may be doped n-type, bottomconfining region 220 may be doped n-type and top confining region 240may be doped p-type.

In another example, in which the LED may emit UV, blue or green light,substrate 210 may comprise Si, SiC, AlN, ZnO, diamond, glass or apolymer, bottom confining region 220, active region 230 and topconfining region 240 may comprise AlxInyGa1-x-yN, with x and y adjustedin each layer such that the bandgap of bottom confining region 220 andtop confining region 240 are larger than the bandgap of the lightemitting layer in active region 230. In some embodiments of this examplesubstrate 210 may be doped n-type, bottom confining region 220 may bedoped n-type and top confining region 240 may be doped p-type.

In some embodiments of the present invention layer structure 250 maycomprise one or more buffer layers (not shown in FIG. 20) formed betweenbottom confining region 220 and substrate 210, the purpose of which isto improve the quality of the subsequently formed bottom confiningregion 220, active region 230 and top confining region 240. In oneexample, in which the LED may emit UV, blue or green light and substrate210 comprises sapphire, additional buffer layers may comprise a lowtemperature GaN or AlxGa1-xN layer and a doped GaN layer. In someembodiments of this aspect of the present invention, layer structure 250may further comprise an insulating layer (not shown) formed over aportion of the layers within layer structure 250 but below active region230. Said insulating layer may result in process simplification becausesubsequent isolation of the individual LED units 110 by removal of aportion of layer structure 250 may only need to be done down to theoptional insulating layer, thus reducing the step height in one or moresteps formed in layer structure 250. Said insulating layer may comprise,for example, AlN or AlxGa1-xN, however this is not a limitation of thepresent invention and in other embodiments said insulating layer maycomprise any material.

FIG. 21 is a cross-sectional view of the structure of FIG. 20 at a laterstage of manufacture. After formation of layer structure 250 (FIG. 20),layer structure 250 and substrate 210 may be patterned usingphotolithography and etching processes. Photolithography processes oroperations involve the use of masks and may sometimes be referred to asmasking operations or acts. The photolithography and etching may includeforming a layer of a radiation-sensitive material, such as photoresist(not shown), over the semiconductor structure, then exposing thephotoresist using, for example, ultraviolet (“UV”) radiation, to form amask, and then etching portions of layer structure 250 using anisotropic or anisotropic etch process such as, for example, wet chemicaletching or a reactive ion etch (“RIE”), to form one or more mesas 410.

In some embodiments of the present invention one or more hard masklayer(s) (not shown) may be formed over layer structure 250 beforepatterning of layer structure 250. Since the photoresist over layerstructure 250 is also etched as part of the etch used to etch portionsof layer structure 250, a hard mask layer or layers may be used toprevent the undesired etching of the upper surface of layer structure250 during the formation of mesa 410. One or more hard mask layers areoptional, and in alternate embodiments, the photoresist layer may bemade relatively thick such that it is not completely eroded during theformation process of mesa 410, and therefore, the photoresist may beused as a masking layer rather than using a hard mask layer. A hard masklayer may comprise, for example, a dielectric such as silicon dioxide(“SiO2”) or silicon nitride (“Si3N4”), or a metal, such as nickel,titanium, aluminum, gold, chromium or the like.

Mesas 410 form LED units 110 as identified in FIGS. 17 and 18. FIG. 22is a top view of the structure of FIG. 21 in accordance with anembodiment of the present invention and FIG. 21 is a cross-sectionalview taken along section line 21-21 of FIG. 22. Referring to FIG. 22,mesas 410 are shown as having a square shape, however this is not alimitation of the present invention and in other embodiments mesa 410may be rectangular, hexagonal, circular or any arbitrary shape. FIG. 22shows all mesas 410 having the same shape, however this is not alimitation of the present invention and in other embodiments a pluralityof shapes for mesa 410 may be employed. FIG. 22 shows each mesa 410being spaced apart from adjacent mesas 410 an equal distance. However,this is not a limitation of the present invention and in otherembodiments the spacing between mesas 410 may not be equal.

Mesas 410 have a top surface 440. In one example, mesa 410 may comprisea square and top surface 440 may have a length in the range of about 75μm to about 1000 μm. In another embodiment mesa 410 may comprise asquare and top surface 440 may have a length in the range of about 200μm to about 500 μm. In some embodiments the spacing between mesas 410may be uniform and be in the range of about 25 μm to about 10,000 μm. Inanother embodiment the spacing between mesas 410 may be uniform and bein the range of about 35 μm to about 200 μM.

In the example shown in FIG. 21, the etch depth (or the height of mesa410) is equal to the thickness of layer structure 250. In other words,surface 430 is the same as the top surface of substrate 210. Howeverthis is not a limitation of the present invention and in otherembodiments, the etch depth may be more or less than that of thethickness of layer structure 250. In an embodiment in which the etchdepth is less than that of the thickness of layer structure 250, surface430 may be formed on a portion of bottom confining region 220 or otheroptional layers as discussed above in reference to FIG. 20. In anembodiment in which the etch depth is more than that of the thickness oflayer structure 250, surface 430 may be formed on a portion of substrate210. As discussed above in reference to FIG. 20, it may be desirable tominimize the height of mesa 410 to simplify subsequent processing.

The sidewalls 420 of mesa 410 may be sloped as shown in FIG. 21 and havea slope in the range of about 20 degrees to about 75 degrees. Howeverthis is not a limitation of the present invention and in otherembodiments sidewalls 420 of mesa 410 may have any angle with respect tosurface 430, including perpendicular or substantially perpendicular tosurface 430.

FIG. 23 is a cross-sectional view of the semiconductor structure of FIG.21 at a later stage of manufacture. FIG. 24 is a top view of thestructure of FIG. 23 in accordance with an embodiment of the presentinvention and FIG. 23 is a cross-sectional view taken along section line23-23 of FIG. 24. After formation of mesas 410 (FIG. 21), a portion ofmesa 410 (FIG. 21) may be removed to expose a portion of bottomconfining region 220 within mesa 410 (FIG. 21). As can be seen from FIG.23, this results in surface region 610 of a portion of bottom confiningregion 220 and surface region 620 of a portion of top confining region240. Surface region 620 may be formed from a portion of surface region440 (FIG. 21) but this is not a limitation of the present invention andin other embodiments surface region 620 may not be formed from a portionof surface region 440 (FIG. 21). As is discussed above with respect tomesa 410 (FIG. 21), the removal of a portion of mesa 410 (FIG. 21) maybe formed using photolithography and etching processes. At this stage ofmanufacture and in subsequent stages, mesa 410 may be referred to as LEDunit 110 (FIG. 17).

Referring to FIG. 24, surface regions 610 and 620 are shown as having arectangular shape, however this is not a limitation of the presentinvention and in other embodiments surface regions 610 and 620 may besquare, hexagonal, circular or any arbitrary shape. As will be discussedlater, the shape of mesa 410 (FIG. 21) and LED unit 110 and surfaceregions 610 and 620 may be configured for optimal device performance,particularly with respect to current spreading and light extraction.FIG. 24 shows all surface regions 610 having the same shape and allsurface regions 620 having the same shape, however this is not alimitation of the present invention and in other embodiments a pluralityof shapes for surface regions 610 and 620 may be employed. FIG. 24 showseach surface region 610 and 620 being positioned in the same location onLED unit 110, however this is not a limitation of the present inventionand in other embodiments surface regions 610 and 620 may be positioneddifferently on different LED units 110. In some embodiments the area ofsurface region 620 may be larger than the area of surface region 610,however this is not a limitation of the present invention and in otherembodiments the area of surface region 620 may be smaller than the areaof surface region 610.

In some embodiments of the present invention LED unit 110 may comprise aplurality of surface regions 610 and/or surface regions 620. In someembodiments of the present invention different surface regions 610 and620 may have the same or different shapes and areas within an individualLED unit 110. The number of surface regions 610 and 620 within mesa 410,as well as their shapes and areas may be configured to achieve optimalLED performance, for example to achieve relatively high currentspreading uniformity or to achieve relatively high luminous intensity,and is not a limitation of the present invention. In some embodiments ofthe present invention, the LED array may comprise a plurality of LEDunits 110 where one or more LED units 110 may have different shapesand/or areas and/or different numbers of surface regions 610 and/or 620.

The difference in height between surface region 610 and surface region620 is sufficient such that all of top confining region 240 and all ormost of all of active region 220 may be removed over surface region 610.In one example surface region 610 is within bottom confining region 220.

A sidewall 630 is formed during the etching process. Sidewall 630 may besloped as shown in FIG. 23 and have a slope in the range of about 20degrees to about 75 degrees. However this is not a limitation of thepresent invention and in other embodiments sidewall 630 may have anyangle with respect to surface 430, including perpendicular orsubstantially perpendicular to surface 430. In the example shown in FIG.23, sidewall 630 is shown as having the same or substantially the sameslope as sidewall 420, however this is not a limitation of the presentinvention and in other embodiments sidewall 630 may have a slopedifferent from the slope of sidewall 420. After removal of a portion ofmesa 410 (FIG. 21), a reduced portion of sidewall 420 may remain on aportion of mesa 410 (FIG. 21), hereinafter referenced as sidewall 420A.

After removal of a portion of mesa 410 (FIG. 21) and formation ofsurface regions 610 and 620, layer 640 may be formed over surface 430,sidewalls 420, 420A and 630 and surface regions 610 and 620. In someembodiments layer 640 may comprise an electrical insulator, however thisis not a limitation of the present invention and in other embodimentslayer 640 may comprise a conductor or a semiconductor. Layer 640 maycomprise, for example, a dielectric material such as silicon dioxide orsilicon nitride or a polymer material, for example polyimide or BCB.Layer 640 may have a thickness ranging from about 50 Å to about 10,000Å. In other embodiments layer 640 may have a thickness ranging fromabout 100 Å to about 1,000 Å.

In some embodiments of the present invention layer 640 may be formedusing techniques such as evaporation, sputtering, chemical vapordeposition (CVD), low pressure chemical vapor deposition (LPCVD),oxidation, spin deposition or the like.

FIG. 25 is a cross-sectional view of the semiconductor structure of FIG.23 at a later stage of manufacture. After formation of layer 640, layer640 may be patterned using photolithography and etching processes toform openings 810 in layer 640, exposing portions of bottom confiningregion 220. In some embodiments the width of openings 810 may be in therange of about 2 μm to about 25 μm, but this is not a limitation of thepresent invention and in other embodiments the width of opening 810 maybe any width.

FIG. 26 is a cross-sectional view of the semiconductor structure of FIG.25 at a later stage of manufacture. After formation of openings 810,bottom electrical contact 910 to bottom confining region 220 may beformed in and/or over openings 810 using well-known semiconductorprocesses. Bottom electrical contact 910 may also be referred to as abottom contact. For example, in some embodiments, bottom electricalcontact 910 may be formed using a lift-off process in which thesemiconductor structure of FIG. 25 is patterned using photolithography,the contact material comprising bottom electrical contact 910 is formedover the photoresist (not shown) and the portions of bottom confiningregion 220 exposed by openings 810 (FIG. 25), the photoresist is removedalong with the contact material formed over the photoresist, leavingcontact material only in openings 810, as shown in FIG. 24, thus formingbottom electrical contact 910. In another example, bottom electricalcontact 910 may be formed by depositing the contact material comprisingbottom electrical contact 910 over the entire semiconductor structureshown in FIG. 23, patterning the contact material using photolithographywith a pattern that leaves the contact material in openings 810 (FIG.25) covered with photoresist, removing the exposed contact material andremoving the resist over the material of bottom electrical contact 910in openings 810 (FIG. 25), thus forming bottom electrical contact 910.These examples are meant to be illustrative and other techniques forcontact deposition may be used as well.

The example shown in FIG. 26 shows bottom electrical contact 910 formedonly within opening 810 (FIG. 25). However, this is not a limitation ofthe present invention and in other embodiments bottom electrical contact910 may extend beyond the edges of openings 810 (FIG. 25), or may notcompletely fill openings 810 (FIG. 25).

Bottom electrical contact 910 may comprise one or more layers. Bottomelectrical contact 910 may comprise metals, silicides or otherconductive materials. The specific material(s) used for bottomelectrical contact 910 will depend on the specific semiconductors inlayer structure 250 (FIG. 20). For example, where layer structure 250(FIG. 20) may comprise GaAs- or GaP-based semiconductors, bottomelectrical contact 910 may comprise Au, Au/Ge or Au/Ge/Ni. For example,where layer structure 250 (FIG. 20) may comprise GaN-basedsemiconductors, bottom electrical contact 910 may Ti/Al. In someembodiments the thickness of bottom electrical contact 910 may be in therange of about 500 Å to about 5000 Å, but this is not a limitation ofthe present invention and in other embodiments bottom electrical contact910 may be any thickness. In some embodiments of the present inventionbottom electrical contact 910 may be formed using techniques such asevaporation, sputtering, chemical vapor deposition (CVD), low pressurechemical vapor deposition (LPCVD), oxidation, spin deposition or thelike.

FIG. 27 is a cross-sectional view of the semiconductor structure of FIG.26 at a later stage of manufacture. After formation of bottom electricalcontact 910, top electrical contact 1010 to top confining region 240 maybe formed in a manner similar to that used to form bottom electricalcontact 910 discussed above and using well-known semiconductorprocesses. In other words, layer 640 may be patterned usingphotolithography and etching processes to form openings (not shown) inlayer 640, exposing portions of top confining region 240 and forming topelectrical contact 1010 in the openings (not shown) in layer 640. Topelectrical contact 1010 may also be referred to as a top contact.

The example shown in FIG. 27 shows top contact 1010 only within theopening in layer 640, however, this is not a limitation of the presentinvention and in other embodiments top contact 1010 may extend beyondthe edges of the opening in layer 640, or may not completely fill theopening in layer 640.

As discussed above with respect to bottom electrical contact 910, topelectrical contact 1010 may comprise one or more layers and may comprisemetals, silicides or other conductive materials. The specificmaterial(s) used for top electrical contact 1010 will depend on thespecific semiconductors in layer structure 250 (FIG. 20). For example,in the example where layer structure 250 (FIG. 20) may compriseGaN-based semiconductors, top electrical contact 1010 may compriseNi/Au. In some embodiments the thickness of top electrical contact 1010may be in the range of about 200 Å to about 5000 Å, but this is not alimitation of the present invention and in other embodiments contactmaterial 1010 may be any thickness. In some embodiments of the presentinvention top electrical contact 1010 may be formed using techniquessuch as evaporation, sputtering, chemical vapor deposition (CVD), lowpressure chemical vapor deposition (LPCVD), oxidation, spin depositionor the like.

In the example shown in FIG. 27 bottom electrical contact 910 and topelectrical contact 1010 are shown in the same location in each LED unit110 (FIG. 17). However, this is not a limitation of the presentinvention and in other embodiments bottom electrical contact 910 and topelectrical contact 1010 may each have different positions on all or someof LED units 110 (FIG. 17).

In the example shown in FIG. 27 bottom electrical contact 910 and topelectrical contact 1010 are shown as having the same rectangular shapein each LED unit 110 (FIG. 17). However, this is not a limitation of thepresent invention and in other embodiments bottom electrical contact 910and top electrical contact 1010 may each have different shapes, forexample a square or circle or any arbitrary shape, or may each havedifferent shapes on all or some of LED units 110 (FIG. 17). Furthermore,in some embodiments of the present invention, bottom electrical contact910 and/or top electrical contact 1010 may have different geometriesthan that shown in FIG. 27 (rectangular), for example they may comprisea serpentine or annular geometry or one contact may enclose or partiallybe interleaved with another or any other geometry.

In some embodiments of the present invention LED unit 110 may compriseone bottom electrical contact 910 and one top electrical contact 1010.However, this is not a limitation of the present invention and in otherembodiments LED unit 110 may comprise a plurality of bottom electricalcontacts 910 and/or a plurality of top electrical contacts 1010. In someembodiments of the present invention, the number of bottom electricalcontacts 910 may be less than, equal to or larger than the number ofsurfaces 610 within a single LED unit 110. In some embodiments of thepresent invention, the number of top electrical contacts 1010 may beless than, equal to or larger than the number of surfaces 620 within asingle LED unit 110.

In some embodiments of the present invention in which LED unit 110comprises a plurality of bottom electrical contacts 910 and/or aplurality of top electrical contacts 1010, each bottom electricalcontact 910 and each top electrical contact 1010 may have the sameshape, size and area. However this is not a limitation of the presentinvention and in other embodiments in which LED unit 110 comprises aplurality of bottom electrical contacts 910 and/or a plurality of topelectrical contacts 1010, each bottom electrical contact 910 and/or eachtop electrical contact 1010 may have a different shape, size or area.

In some embodiments of the present invention, one or more heattreatments may be required to achieve acceptable ohmic contact betweentop electrical contact 1010 and top confining region 240 and betweenbottom electrical contact 910 and bottom confining region 220.Acceptable ohmic contact may mean a specific contact resistance of lessthan 1E-3 Ω-cm2, or less than 1E-4 Ω-cm2. Such heat treatments may beperformed, for example, in a furnace, on a hot plate, in a rapid thermalanneal system or the like. Annealing temperatures may range from about300° C. to about 800° C., however the method and time and temperature ofthe anneal process are not limitations of the present invention and inother embodiments, other annealing methods, temperatures or temperatureprofiles, or times may be used. In some embodiments of the presentinvention, the anneal process for bottom electrical contact 910 may beperformed prior to the formation of top electrical contact 1010. Inother embodiments of the present invention, top electrical contact 1010may be formed and annealed before formation and anneal of bottomelectrical contact 910. In all cases, it is important to note that thefirst-formed contact will also receive the anneal process from thesecond-formed contact. In some embodiments of the present invention, oneanneal step may be carried out after formation of both bottom electricalcontact 910 and top electrical contact 1010. Annealing may be done in aninert ambient, for example nitrogen, a reducing ambient, for exampleforming gas, or any other ambient; the annealing ambient is not alimitation of the present invention.

In some embodiments of the present invention, it may be desirable tominimize the annealing temperature and/or time or to eliminate theannealing altogether, for example when top contact 1010 and/or bottomcontact 910 also act as a mirror (discussed below). In this example,reduced annealing temperatures and/or elimination of the annealing stepor steps altogether may provide a higher reflectivity to a wavelength oflight emitted by the light-emitting device.

In some embodiments of the present invention bottom electrical contact910 and top electrical contact 1010 may be formed from the same materialin the same series of process steps. For example, openings 810 (FIG. 25)in layer 640 (FIG. 25) for bottom electrical contact 910 (FIG. 26) andopenings in layer 640 (not shown) for top electrical contact 1010 (FIG.27) may be formed in one step, followed by formation of bottomelectrical contact 910 and top zoos electrical contact 1010 in one setof steps from the same material or materials.

FIG. 28 is a cross-sectional view of the semiconductor structure of FIG.27 at a later stage of manufacture. After formation of top contact 1010,interconnect layer 1110 may be formed in a manner similar to that usedto form bottom electrical contact 910 and top electrical contact 1010discussed above and using well-known semiconductor processes. In otherwords, the material comprising interconnect layer 1110 may be patternedusing photolithography and etching processes to couple top electricalcontacts 1010 and bottom electrical contacts 910 as desired and to formterminals 120A (FIG. 17) and 120B (FIG. 17). Top contact 1010 and bottomcontact 910 of individual LED units 110 (FIG. 17) may be coupled in anyway, as was discussed previously; the connection topology is not alimitation of the present invention. For example, in some embodiments ofthe present invention, the individual LED units 110 (FIG. 17) may becoupled in series as shown in FIG. 10C, in parallel as shown in FIG. 10Bor a combination of series and parallel connections as shown in FIG.10D. In some embodiments, a portion or all of the individual LED units110 (FIG. 17) may be coupled anode to cathode as shown in FIGS. 10A to10D while in other embodiments contact regions 120A and 120B may eachhave both one or more anodes and one or more cathodes of individual LEDunits 110 (FIG. 17) coupled to them as shown in FIG. 10E, and in otherembodiments, a combination of these types of couplings may be utilized.In the example shown in FIG. 17, the LED light engine comprises twostrings of individual LED units 110 coupled in parallel, with eachstring comprising two individual LED units 110 coupled in series asshown in FIG. 10A.

In some embodiments of the present invention interconnect 1110 may beformed using techniques such as evaporation, sputtering, chemical vapordeposition (CVD), low pressure chemical vapor deposition (LPCVD),oxidation, spin deposition or the like. In some embodiments of thepresent invention interconnect 1110 may comprise more than one layer.Interconnect 1110 may have a thickness in the range of about 0.05 μm toabout 1.0 μm, however this is not a limitation of the present inventionand in other embodiments, layer 1110 may have any thickness.

In some embodiments of the present invention bottom electrical contact910 and/or top electrical contact 1010 may comprise a material that alsoacts as a mirror for light of a wavelength generated by the LED to whichit is attached, reflecting light back from the contacts and out throughsurface 140 (FIG. 17). In yet additional alternative embodiments, bottomelectrical contact 910 and/or top electrical contact 1010 may comprise amaterial that acts as a mirror and one or more additional mirror layers(not shown) may be formed over all of or portions of back electricalcontact 910 and/or top electrical contact 1010. In these embodiments,the additional mirror may extend beyond bottom electrical contact 910and top electrical contact 1010 and cover portions of or all of theadditional surfaces of individual LED units 110 and the regions betweenindividual LED units 110. In some embodiments interconnect 1110 maycomprise a material that also acts as a mirror for light of a wavelengthgenerated by the LED to which it is attached. In some embodiments,materials that act as a mirror for light of a wavelength generated bythe LED to which it is attached may be formed over portions of or all orsubstantially all surfaces of LED units 110 and all regions in betweenLED units 110. In some embodiments of the present invention, all orportions of the material comprising top electrical contact 1010 and/orbottom electrical contact 910 may be left in place outside of openings810 (FIG. 25) and the opening for top electrical contact 1010 (notshown) to form a mirror over all or portions of the semiconductorstructure.

Mirrors envisioned for use in the embodiments of the present inventioncomprise a reflective surface that reflects light of a wavelengthemitted by the LED. In embodiments where the mirror is not formed bybottom electrical contact 910 and/or top electrical contact 1010 and/orinterconnect 1110, exemplary mirrors may comprise a Bragg reflector, ormay comprise a metal or metal alloy thin film, for example made up ofone or more of the following materials: Au, Ag, Pt, Pd, Ti, and/or Ni,or alloys thereof. However, it should be recognized that numerousmethods and materials can be used to make satisfactory mirrors, andthese examples do not represent limitations on the invention.

FIG. 29 is a cross-sectional view of the semiconductor structure of FIG.28 at a later stage of manufacture. After formation of interconnectlayer 1110, layer 1210 may be formed over interconnect layer 1110 andportions of layer 640. Layer 1210 may be an insulator and may be used toprovide electrical isolation between various portions of interconnectlayer 1110 and subsequently formed layers 1410, 1520 and carrier 1510(FIG. 17). Layer 1210 may comprise, for example, a dielectric, forexample silicon dioxide or silicon nitride, a semiconductor, for exampleAlN, SiC, silicon, polysilicon or diamond, or a polymer, for examplepolyimide or benzocyclobutene (BCB). In some embodiments of the presentinvention, layer 1210 may be chosen to have a relatively high thermalconductivity and/or a relatively high resistivity. For example, in someembodiments of the present invention layer 1210 may have a resistivityhigher than 1E4 Ω-cm, or higher than 1E5 Ω-cm, or higher than 1E6 Ω-cm.However, this is not a limitation of the present invention and in otherembodiments layer 1210 may be semiconducting or conductive. In someembodiments of the present invention layer 1210 may have a thermalconductivity higher than 0.01 W/cm-K, or higher than 0.1 W/cm-K, orhigher than 1 W/cm-K. Layer 1210 may be formed using a variety oftechniques such as evaporation, sputtering, plating, CVD, or LPCVD. Theformation process of layer 1210 is not a limitation of the presentinvention and in other embodiments any method of forming layer 1210 maybe used. In some embodiments layer 1210 may have a relatively smallthickness, to provide a small thermal resistance and/or electricalresistance between LED units 110 (FIG. 17) and layer 1410 (FIG. 17). Insome examples, layer 1210 may have a thickness less than 200 nm, or lessthan 100 nm or less than 50 nm. In the example shown in FIG. 29, layer1210 covers all of the top surface of semiconductor structure 100.However, this is not a limitation of the present invention and in otherembodiments of the present invention, layer 1210 may cover only portionsof the top surface of semiconductor structure 100 at the stage shown inFIG. 29, for example in some embodiments layer 1210 may only cover thesurface of region 1320 of LED unit 110 (FIG. 30).

FIG. 30 is a cross-sectional view of the semiconductor structure of FIG.29 at a later stage of manufacture. After formation of layer 1210,filler material 1310 may be formed over layer 1210. One purpose offiller material 1310 may be to provide mechanical support for LED units110 (FIG. 17) and or portions of interconnect 1110 during optionalsubsequent removal of substrate 210 and to fill gaps between LED units110 (FIG. 17) and subsequently mounted carrier 1510 (FIG. 17) andassociated attachment layers 1520 (FIG. 17) and 1410 (FIG. 17). Fillermaterial 1310 may comprise, for example, a dielectric, for examplesilicon dioxide or silicon nitride, a semiconductor, for example AlN,SiC, silicon, polysilicon or diamond, or a polymer, for examplepolyimide or BCB. In some embodiments of the present invention, fillermaterial 1310 may be chosen to have a relatively high thermalconductivity and/or a relatively high resistivity. For example, in someembodiments of the present invention filler material 1310 may have aresistivity higher than 1E4 Ω-cm, or higher than 1E5 Ω-cm, or higherthan 1E6 Ω-cm, however this is not a limitation of the present inventionand in other embodiments filler material 1310 may be semiconducting orconductive. In some embodiments of the present invention, fillermaterial 1310 may act as an electrical conductor and provide one or morepathways for power and/or signals to LED units 110. In some embodimentsof the present invention filler material 1310 may have a thermalconductivity higher than 0.01 W/cm-K, or higher than 0.1 W/cm-K, orhigher than 1 W/cm-K. Filler material 1310 may be formed using a varietyof techniques such as spin deposition, evaporation, sputtering, plating,CVD, or LPCVD. The formation process of filler material 1310 is not alimitation on the present invention and in other embodiments any methodof forming filler material 1310 may be used.

FIG. 30 shows the top surface of filler material 1310 as coplanar withthe surface 1330 of portion 1320 of LED unit 110. In other words,surface 1330 of portion 1320 of LED unit 110 is exposed and not coveredby filler material 1310. In this example filler material 1310 may beformed and patterned for selective removal over surface 1330 of portion1320 of LED unit 110. In other embodiments filler material 1310 may beformed using a technique such that it acts to planarize the top surfaceof structure 100, but does not cover surface 1330 of portion 1320 of LEDunit 110. In such an embodiment filler material 1310 may be formed, forexample, using a spin deposition process or formed over the entiresurface of semiconductor structure 100, for example by evaporation,sputtering, spin deposition, CVD or LPCVD, followed by polishing orplanarizing using, for example chemical mechanical polishing (CMP) toexpose surface 1330 of portion 1320 of LED unit 110.

FIG. 30 shows the top surface of filler material 1310 as coplanar withsurface 1330 of portion 1320 of LED unit 110, however this is not alimitation of the present invention. In some embodiments of the presentinvention filler material 1310 may have a top surface that is above orbelow surface 1330 of portion 1320 of LED unit 110. In some embodimentsof the present invention, layer 1210 and filler material 1310 may be thesame material. In some embodiments filler material 1310 may berelatively soft or compliant, for example filler material 1310 maycomprise a polymer, and filler material 1310 may act to reduce stress insemiconductor structure 100 after subsequent attachment to carrier 1510(FIG. 17). In some embodiments of the present invention, layer 1210and/or filler material 1310 may be optional. In some embodiments of thepresent invention all or some layers may be chosen on the basis of theirproperties to improve overall device yield and/or performance. In someembodiments of the present invention layers that are provided in anexample as a single material may comprise a plurality of materialschosen on the basis of their properties to improve overall device yieldand/or performance. For example, in some embodiments of the presentinvention layer 1210 and filler material 1310 may comprise a pluralityof layers of different materials to reduce the overall strain and/or toincrease the mechanical strength of semiconductor structure 100. Inanother embodiment of the present invention, layer 1210, filler material1310 and attachment layers 1410 (FIG. 17) and 1520 (FIG. 17) maycomprise a plurality of layers of different materials that may provideincreased transfer of heat from LED units 110 to carrier 1510 (FIG. 17).

In the example shown in FIG. 30, filler material 1310 is shown as beingpresent between all LED units 110. However, this is not a limitation ofthe present invention and in other embodiments of the present inventionfiller material 1310 may only be present between a portion of LED units110.

In a subsequent step the semiconductor structure of FIG. 30 may beattached to a carrier 1510 which is shown in FIG. 32. FIG. 31 is across-sectional view of the semiconductor structure of FIG. 30 at alater stage of manufacture. After formation of filler material 1310,attachment layer 1410 may be formed over filler material 1310 andsurfaces 1330 of portion 1320 of LED unit 110. Referring now to FIG. 32,FIG. 32 is a cross-sectional view of carrier 1510 with attachment layer1520 formed over carrier 1510. Attachment layer 1520 (FIG. 32) and 1420(FIG. 31) may be used to attach the semiconductor structure of FIG. 29to carrier 1510 (FIG. 32).

In one example attachment layer 1410 may comprise a solder, for examplean Au/Sn solder, an In solder or an In/Sn solder. The number of elementsin the solder and the composition of the solder are not a limitation ofthe present invention and in other embodiments, attachment layer 1410may comprise any type of solder or composition of solder. In otherembodiments of the present invention, attachment layer 1410 may comprisea glue or adhesive; the type of glue or adhesive is not a limitation ofthe present invention and in other embodiments attachment layer 1410 maycomprise any type of glue or adhesive. In the example where attachmentlayer 1410 may comprise a solder, for example an Au/Sn solder,attachment layer 1520 may comprise a layer to which a solder may form asuitable bond, for example a metal such as Au, Sn, or other metals. Insome embodiments of the present invention attachment layer 1410 and/orattachment layer 1520 may be formed using, for example, evaporation,plating, sputtering, CVD, LPCVD, screen printing, dispensing or othertechniques. In some embodiments of the present invention attachmentlayer 1410 and/or attachment layer 1520 may each have a thickness in therange of about 5 nm to about 5 μm. In some embodiments of the presentinvention attachment layer 1410 and/or attachment layer 1520 may eachhave a thickness in the range of about 0.25 μm to about 3 μm.

In some embodiments of the present invention, attachment layer 1410and/or attachment layer 1520 may have a relatively high thermalconductivity and may provide a pathway for heat removal from activeregions 230 of LED units 110. In some embodiments of the presentinvention attachment layer 1410 and/or attachment layer 1520 may have athermal conductivity higher than 0.5 W/cm-K, or higher than 1 W/cm-K. Insome embodiments of the present invention, attachment layer 1410 and/orattachment layer 1520 may have a relatively high resistivity, forexample higher than 1E4 Ω-cm, or higher than 1E5 Ω-cm, or higher than1E6 Ω-cm, however this is not a limitation of the present invention andin other embodiments attachment layer 1410 and/or attachment layer 1520may be semiconducting or conductive. In some examples of thisembodiment, layer 1210 may be optional.

In some embodiments of the present invention, attachment layer 1410and/or attachment layer 1520 may each comprise a plurality of layers. Insome embodiments of the present invention, only one attachment layer maybe utilized and this may be formed over either semiconductor structure100 or over carrier 1510.

After the deposition of attachment layer 1410 (FIG. 31) and/orattachment layer 1520 (FIG. 32) and prior to the attachment ofsemiconductor structure 100 (FIG. 31) to carrier 1510 (FIG. 32),attachment layer 1410 (FIG. 31) and/or attachment layer 1520 (FIG. 32)may be polished or planarized using, for example, chemical mechanicalpolishing (CMP), to form a relatively high quality bond during theattachment step.

In the example shown in FIG. 31, attachment layer 1410 is shown ascovering filler material 1310 and surfaces 1330 of portion 1320 of LEDunit 110, in other words attachment layer 1410 is shown as covering theentire surface of semiconductor structure 100 as shown in FIG. 31.However, this is not a limitation of the present invention and in otherembodiments of the present invention attachment layer 1410 may coveronly portions of filler material 1310 and surfaces 1330 of portion 1320of LED unit 110. In some embodiments of the present invention,attachment layer 1410 may act as an electrical conductor and provide oneor more pathways for power and/or signals to LED units 110.

Referring now to FIG. 32, FIG. 32 is a cross-sectional view of carrier1510 with attachment layer 1520 formed over carrier 1510. Carrier 1510may comprise an insulator, a semiconductor or a conductor. Carrier 1510may comprise, for example a semiconductor such as AlN, SiC, silicon,polysilicon, GaAs, GaP, InP, sapphire, diamond or other semiconductorsand may be doped or undoped depending on the application, although themethods and apparatuses described herein are not limited in this regard.In other embodiments of the present invention, carrier 1510 may compriseother materials such as, for example, glass, polymers or metals. Carrier1510 may have a thickness ranging from about 50 micron (μm) to about2,000 μm, but this is not a limitation of the present invention and inother embodiments the substrate may have any thickness. The thickness ofcarrier 1510 may be reduced through subsequent thinning processes insome embodiments. In some embodiments of the present invention carrier1510 may comprise more than one material, for example a layer of a firstmaterial formed over a second material. In one example such a carriermay comprise an electrical insulator formed over an electricalconductor. Carrier 1510 may be absorbing to or substantially transparentat a wavelength of light generated by the light-emitting device.

Carrier 1510 may have a diameter in the range of about 1″ to over 12″,however the diameter of carrier 1510 is not a limitation of the presentinvention and in other embodiments carrier 1510 may have any diameter.It may be desirable for carrier 1510 to have a diameter the same as, orsubstantially the same as substrate 210 (FIG. 31) however this is not alimitation of the present invention and in other embodiments, carrier1510 may have a diameter larger than or smaller than the diameter ofsubstrate 210 (FIG. 31).

In some embodiments of the present invention carrier 1510 may have acircular shape, like that often used for conventional semiconductorprocessing. However this is not a limitation of the present inventionand in other embodiments carrier 1510 may be square, rectangular or haveany arbitrary shape. In some embodiments of the present invention theshape and size of carrier 1510 may be the same as, or substantially thesame as that of substrate 210 (FIG. 31). However this is not alimitation of the present invention and in other embodiments carrier1510 and substrate 210 may have different shapes and sizes.

In some embodiments of the present invention, carrier 1510 may have arelatively high thermal conductivity and may provide a pathway for heatremoval from active regions 230 of LED units 110. In some embodiments ofthe present invention carrier 1510 may have a thermal conductivityhigher than 0.15 W/cm-K, or higher than 0.5 W/cm-K, or higher than 1W/cm-K. In some embodiments of the present invention, carrier 1510 mayhave a relatively high resistivity, for example greater than 1E4 Ω-cm,or greater than 1E5 Ω-cm, or greater than 1E6 Ω-cm, however this is nota limitation of the present invention and in other embodiments carrier1510 may be semiconducting or conductive.

In the example shown in FIG. 32 attachment layer 1520 is shown ascovering the entire surface of carrier 1510. However, this is not alimitation of the present invention and in other embodiments of thepresent invention, attachment layer 1520 may cover only portions ofcarrier 1510. In some embodiments of the present invention, attachmentlayer 1520 may act as an electrical conductor and provide one or morepathways for power and/or signals to LED units 110.

FIG. 33 is a cross-sectional view of the semiconductor structure of FIG.31 at a later stage of manufacture. After formation of attachment layer1410, and formation of attachment layer 1520 over carrier 1510 (FIG.32), surface 1420 of the semiconductor structure of FIG. 31 and surface1530 of the carrier of FIG. 32 may be joined or attached, as shown inFIG. 33. The method of joining depends on the materials used forattachment layers 1410 and 1520. In some embodiments, the joining may beperformed using thermocompression bonding, wafer bonding, adhesive,glue, solder or the like. In the example where attachment layer 1410comprises an Au/Sn solder and attachment layer 1520 comprises Au,joining may be accomplished using a combination of heat and pressure, inother words using thermocompression bonding. In the case whereattachment layer 1420 and/or attachment layer 1510 comprise a glue oradhesive, joining may be accomplished by mating surface 1420 (FIG. 31)and surface 1530 (FIG. 32) and the optional application of pressureand/or heat.

FIG. 34 is a cross-sectional view of the semiconductor structure of FIG.33 at a later stage of manufacture. After joining surface 1420 of thesemiconductor structure of FIG. 31 and surface 1530 of the carrier ofFIG. 32, a portion or all of substrate 210 may be optionally removed. Inthe example shown in FIG. 32, all of substrate 210 is removed. Substrate210 may be removed using techniques such as lapping and polishing, CMP,wet chemical etching, reactive ion etching (RIE), laser lift-off or thelike. In some embodiments of the present invention, removal of substrate210 may comprise more than one step.

In some embodiments of the present invention a portion of substrate 210may be removed. FIG. 35 shows an example semiconductor structure 200 inwhich a portion of substrate 210 has been removed. Such an approach maybe used when substrate 210 is either absorbing or substantiallytransparent at a wavelength of light generated by the light-emittingdevice. In some embodiments of the present invention semiconductorstructure 200 may be formed from the semiconductor structure of FIG. 33.

In some embodiments of the present invention in which a portion ofsubstrate 210 may be removed, as shown in FIG. 35, a material reflectiveto a wavelength of light emitted by LED unit 110 may be optionallyformed over all of or portions of sidewalls 1910. Such a reflectivematerial may be especially applicable when substrate 210 may comprise amaterial that may be absorbing to a wavelength of light emitted by LEDunit 110. In some embodiments of the present invention such reflectivematerial may comprise a Bragg reflector, or may comprise a metal ormetal alloy thin film, for example made up of one or more of thefollowing materials: Au, Ag, Pt, Pd, Ti, and/or Ni, or alloys thereof.However, it should be recognized that numerous methods and materials canbe used to make satisfactory mirrors, and these examples do notrepresent limitations on the invention.

In some embodiments of the present invention in which substrate 210(FIG. 20) may comprise a material that may be transparent and ortranslucent to a wavelength of light emitted by LED unit 110, all ofsubstrate 210 (FIG. 20) may be left in place and the light emitted byLED units 110 may be transmitted from LED units 110 through substrate210 (FIG. 20). In some embodiments of the present invention whereinsubstrate 210 (FIG. 20) may be transparent to a wavelength of lightemitted by LED unit 110, light extraction features may be formed insubstrate 210 (FIG. 20) and/or at the interface of substrate 210 (FIG.20) and layer structure 250 (FIG. 20) or within a region of layerstructure 250 (FIG. 20) adjacent to substrate 210 (FIG. 20 to improvethe light extraction efficiency. In some embodiments of the presentinvention, light extraction features may comprise one or moreanti-reflection coatings and/or surface roughening, texturing,patterning, imprinting or the like. In some examples such lightextraction features may be formed in a regular periodic array, howeverthis is not a limitation of the present invention and in otherembodiments, light extraction features may be formed in a random orsemi-random pattern.

Removal of substrate 210 (FIG. 20) may be desirable to provide increasedlight extraction from LED units 110. If substrate 210 is left in place,then an interface between two materials with potentially differentindices of refraction (substrate 210 and layer structure 250) may exist,causing a reduction in light extraction due to TIR and additionalabsorption, as discussed with respect to FIG. 5. Removal of substrate210 and formation of an index matched layer over LED units 110 or theentire light engine may result in increased light extraction and thusluminous efficacy.

FIG. 36 is a cross-sectional view of the semiconductor structure of FIG.34 at a later stage of manufacture. After optional removal of portionsof or all of substrate 210, optional light conversion material 1810 maybe formed over surface 140 (inclusive or exclusive of the exposedportions of layer 640). Optional light conversion material 1810 maycomprise organic or inorganic phosphors or other materials capable ofabsorption of all of or a portion of the light emitted from activeregion 230 and re-emitting it at a different wavelength. In someembodiments of the present invention light conversion material 1810 maycomprise a down conversion material and in other embodiments lightconversion material 1810 may comprise an up conversion material.

In some embodiments of the present invention light conversion materialmay be formed by evaporation, screen printing, ink jet printing, otherprinting methods, CVD, spin deposition or the like. In some embodimentsof the present invention, optional light conversion material 1810 may besuspended or embedded in a second material (not shown), and in someembodiments the second material may comprise a material with an index ofrefraction between that of the material in layer structure 250 (FIG. 20)and air. In one example of this embodiment such second material maycomprise an epoxy, gel or resin with an index of refraction in the rangeof about 1.2 to about 1.7. Such a second material may act to reducetotal internal reflection and increase the light extraction efficiencyof the light engine.

In FIG. 36, light conversion material 1810 is shown as being formed overthe entirety of surface 140, however this is not a limitation of thepresent invention and in other embodiments light conversion material1810 may be formed over a portion of surface 140, and in particular maybe formed over portions of surface 140 under LED units 110. In someembodiments of the present invention light conversion material 1810 maybe formed over portions of LED units 110, such that a portion of thelight emitted by active region 230 exits LED unit 110 directly and aportion of the light emitted by active region 230 is absorbed in andthen re-emitted by light conversion material 1810.

In some embodiments of the present invention light conversion material1810 may comprise a plurality of layers or a mixture of different typesof light conversion materials. In some embodiments of the presentinvention, a first light conversion material may be formed over a firstportion of LED units 110 and a second light conversion material may beformed over a second portion of LED units 110. In one example, a firstportion of LED units 110 may be covered with a first light conversionmaterial 1810 that when mixed with the light emitted from the firstportion of LED units 110 produces a warm white color and a secondportion of LED units 110 may be covered with a second light conversionmaterial 1810 that when mixed with the light emitted from the secondportion of LED units 110 produces a cool white color. In one example ofthis embodiment, the LED units associated with the first and secondlight conversion materials may be separately addressable, and thus alight having either warm or cool properties may be created by separatelyturning on LED units 110 associated with either the warm or cool lightconversion materials respectively. In this example two sub-arrays of LEDunits 110 and two types of light conversion materials 1810 arediscussed, however this is not a limitation of the present invention andother embodiments may comprise three or more sub-arrays of LED units 110and three or more different light conversion materials 1810. In thisexample two types of white light, cool and warm are discussed, howeverthis is not a limitation of the present invention and in otherembodiments multiple colors may be produced using this approach.

Referring now to FIG. 37, FIG. 37 is a cross-sectional view of thesemiconductor structure of FIG. 36 at a later stage of manufacture.After optional formation of light conversion material 1810, a portion ofoptional light conversion material 1810 and a portion of layer 640 maybe removed, exposing portions of interconnect layer 1110, hereinidentified in FIGS. 37, 17 and 18 as contact regions 120A and 120B.Optional filler material 1310 may provide mechanical support to contactareas 120A and 120B. Portions of light conversion material 1810 andlayer 640 may be removed using, for example, patterning and etchingtechniques discussed previously. Connection to the light engine may bemade through contact regions 120A and 120B.

At this point in the manufacture of the semiconductor structure shown inFIG. 37, a plurality of complete light engines is formed on carrier1510. FIGS. 17-37 have shown a process flow for manufacturing oneembodiment of the light engine of the present invention; a schematic ofthe entire wafer at this stage of manufacture is shown in FIG. 38. FIG.38 shows a top view of the entire wafer at this stage of manufacture,comprising carrier 1510 and a plurality light engines 3610 formed oncarrier 1510 spaced apart from each other by streets 3620. Streets 3620may have a width in the range of about 5 μm to about 500 μm. Howeverthis is not a limitation of the present invention and in otherembodiments, streets 3620 may have any width.

After removal of portion of light conversion material 1810 and a portionof layer 640 and exposing portions of interconnect layer 1110,individual light engines 2210 may be separated from the semiconductorstructure of FIG. 38. In other words, the semiconductor structure ofFIG. 38 comprises a wafer of light engines and the light engines areseparated or singulated from the wafer to form separate light engines asshown in FIG. 17. Singulation may be performed using methods such aslaser cutting, laser scribing, mechanical scribe and break or dicing.However, this is not a limitation of the present invention and in otherembodiments other methods of separation or singulation may be used.

FIG. 38 shows all light engines 3610 formed on carrier 1510 as havingthe same size. However this is not a limitation of the present inventionand in other embodiments, more than one size light engine may be formedon carrier 1510. In some embodiments of the present invention, differentlight engines formed on carrier 1510 may have different characteristics.For example they may have a different size, a different number of LEDunits, a different color or spectral distribution and thecharacteristics and variation of the characteristics of the lightengines on carrier 1510 are not a limitation of the present invention.

FIG. 17 shows contact regions 120A and 120B positioned adjacent to thearray of LED units 110. However, this is not a limitation of the presentinvention and in other embodiments, contact regions 120A and 120B mayhave any shape, size or position. For example, FIG. 39 is a schematic ofan embodiment of the present invention in which two LED units 110 arereplaced by contact regions 120A and 120B. FIG. 17 shows one contactregion 120A and one contact region 120B. However this is not alimitation of the present invention and in other embodiments the lightengine (semiconductor structure 100) may comprise a plurality of contactregions 120A and/or a plurality of contact regions 120B.

FIG. 40 is a top view of an embodiment of the present inventioncomprising bottom electrical contact 910 that extend aroundsubstantially three sides of top electrical contact 1010. As can be seenin FIG. 40 current must flow from bottom electrical contact 910laterally through bottom confining region 220 and then up and out of LEDunit 110 through active region 230, to confining region 240 and topelectrical contact 1010. Extending bottom electrical contacts 910 aroundmore of top electrical contact 1010 may result in improved currentspreading and reduced forward voltage. The example in FIG. 40 showsbottom electrical contact 910 extending around substantially three sidesof top electrical contact 1010. However this is not a limitation and inother embodiments bottom electrical contact 910 may extend a lesser orgreater portion of top electrical contact 1010 than shown in FIG. 40. Insome embodiments of the present invention bottom electrical contact 910may extend around all of or substantially all of top contact 1010.

Another aspect of the semiconductor structure of FIG. 40 is thatsegments of interconnect 1110 cover a relatively large portion orsubstantially all of the surface. In some embodiments of the presentinvention bottom electrical contact 910 and/or top electrical contact1010 and/or interconnect 1110 may be reflective to a wavelength of lightemitted by LED unit 110 and thus act to reflect light emitted by LEDunit 110 back through all or portions of layer structure 250 within LEDunit 110 and out of the light engine. In some embodiments of the presentinvention interconnect 1110 may comprise a Bragg reflector, or maycomprise a metal or metal alloy thin film, for example made up of one ormore of the following materials: Au, Ag, Pt, Pd, Ti, and/or Ni, oralloys thereof. However, it should be recognized that numerous methodsand materials can be used to make a reflective interconnect and/orcontact, and these examples do not represent limitations on theinvention.

In the example shown in FIGS. 17-40, bottom electrical contact 910 isshown as being formed on a portion of bottom confining region 220opposite substrate 210. However, this is not a limitation of the presentinvention and in other embodiments bottom electrical contact 910 may beformed on the opposite side of bottom confining region 220. For example,FIG. 41 is a schematic of an embodiment of the present invention inwhich semiconductor structure 300 is at a stage of manufacture afterremoval of substrate 210 but before formation of optional lightconversion material 1810. In the example shown in FIG. 41, contact tobottom confining region 220, identified as 910A, couples bottomconfining region 220 to a portion of interconnect layer 1110, thuselectrically coupling top electrical contact 1010 of a first LED unit110 and bottom electrical contact 910A of a second LED unit 110A. In theexample shown in FIG. 41, an optional layer 3910 is formed over thesurface exposed after removal of substrate 210 but before formation ofbottom electrical contacts 910A. In some embodiments of the presentinvention layer 3910 may comprise a current spreading layer to aid inuniform distribution of current from contact 910A to bottom confiningregion 220. In some embodiments of the present invention layer 3910 maycomprise a protection layer to aid in protection of the underlying lightengine. In some embodiments of the present invention layer 3910 maycomprise a plurality of layers. In some embodiments of the presentinvention layer 3910 may comprise a current spreading layer and aprotection layer. Examples of current spreading layers may include ITOor other transparent conductive oxides, very thin layers of metal suchas Ni or Au, or the like. Examples of protection layers may includesilicon dioxide, silicon nitride or other such dielectric materials orother materials transparent to a wavelength of light emitted by LED unit110. However, this is not a limitation of the present invention and inother embodiments, layer 3910 may be omitted. In some embodiments of thepresent invention, layer 3910 may be formed before bottom contact 910Aand in some embodiments of the present invention layer 3910 may beformed after bottom contact 910A. In some embodiments of the presentinvention layer 3910 may overlap bottom contact 910A. In someembodiments of the present invention bottom contact 910A may overlaplayer 3910.

In the example shown in FIG. 41, bottom electrical contact 910A is shownas coupling bottom confining region 220 and interconnect layer 1110.However, in other examples, bottom electrical contact 910A may be formedonly over a portion of bottom confining region 220 and a separateconductor may couple bottom contact 910A to interconnect layer 1110. Insome embodiments of this example, contact regions 120A (FIG. 17) and120B (FIG. 17) may be formed from a portion of bottom contacts 910Aand/or a portion of interconnect 1110. In other embodiments of thisexample, an additional patterning and metallization step may be utilizedfor formation of contact regions 120A (FIG. 17) and 120B (FIG. 17). Notethat in this embodiment of the present invention, only one mesaformation step may be required. This may result in a larger lightemitting area of LED unit 110 for a given overall size of LED unit 110.

FIG. 42 shows a cross-sectional view of a variation of the semiconductorstructure of FIG. 41. In the structure shown in FIG. 42 bottomelectrical contact to bottom confining region 220 may be made on thesidewall of the mesa defining each LED unit 110, and is identified inFIG. 42 as 910B. In FIG. 42 bottom electrical contact 910B is shown ascomprising the same material as interconnect 1110, however this is not alimitation of the present invention and in other embodiments a separatecontact to bottom confining region 220 may be formed (not shown) andelectrically coupled to interconnect 1110. In FIG. 42 contact area 120Aand 120B are shown as comprising the same material as interconnect 1110,however this is not a limitation of the present invention and in otherembodiments a separate layer may be formed for contact area 120A and120B (not shown) and electrically coupled to interconnect 1110. In FIG.42 layer 3910 is shown as covering all of the exposed portion of bottomconfining region 220, however this is not a limitation of the presentinvention and in other embodiments layer 3910 may cover only a portionof the exposed portion of bottom confining region 220. Note that in FIG.42 layer 3910 is coupled to bottom contact 910B to provide improvedcurrent spreading through bottom confining region 220.

The structures shown in FIGS. 41 and 42 may have several advantages overthe structure shown in FIG. 17 including fewer processing steps, highermanufacturing yield, lower manufacturing cost, a larger light emittingarea resulting in an increased light output and a larger p contact andassociated mirror or reflective surface leading to improved currentspreading and light extraction and thus an improved luminous efficacyand improved current spreading over bottom confining region 220 leadingto an improved luminous efficacy. In some embodiments of the presentinvention the mirrors or reflective surfaces associated with thep-contact in the structures shown in FIGS. 41 and 42 may be lesssensitive to degradation than the p-mirrors shown in FIG. 17.

FIG. 44 is a top view of structure 400 of FIG. 43 in accordance withanother embodiment of the present invention and FIG. 43 is across-sectional view taken along section line 43-43 of FIG. 44.Referring to FIG. 43, structure 400 comprises a plurality of LED units4220 formed over substrate or carrier 4210, conductive elements 4230 andcontact areas 4250A and 4250B. LED units 4220 comprise a bottomconfining region 4260 formed over substrate 4210, an active region 4264formed over bottom confining region 4260 and a top confining region 4268formed over active region 4264. Bottom confining region 4260, activeregion 4264 and top confining region 4268 comprise layer structure 4270.A top contact 4234 may be formed over a portion of top confining region4268 and a bottom contact 4236 may be formed over a portion of bottomconfining region 4260. Conductive elements 4230 electrically couple LEDunits 4220 to each other and to contact areas 4250A and 4250B. Incontrast to the structure shown in FIG. 17, structure 400 may emit lightfrom the top, sides and, if substrate or carrier 4210 is transparent,the bottom.

In some embodiments of the present invention, the structure shown inFIG. 20 may serve as a starting point for the manufacture of structure400 of FIG. 43 and the process up to FIG. 23 may be the same as thatused to manufacture the structure in FIG. 17. After formation of thestructure in FIG. 23, top contact 4234 and bottom contact 4236 may beformed in a manner similar to that described previously, for exampleusing deposition and etching or liftoff techniques. In some embodimentsof the present invention, the dimensions of and material comprising topcontact 4234 and bottom contact 4236 may be the same as discussed withreference to the structure in FIG. 17. Referring now to FIG. 44, LEDunits 4220 are shown in this example as being electrically coupled in aconfiguration similar to that of FIG. 10D. However this is not alimitation of the present invention and in other embodiments otherconfigurations may be used.

LED units 4220 are shown in FIGS. 43 and 44 as being electricallycoupled using bonding wire, for example Au bonding wire, but this is nota limitation of the present invention and in other embodiments othermethods of electrical coupling may be used, for example air bridge,metallization lines, or the like.

LED units 4220 are shown in FIGS. 43 and 44 as being completely coveredby optional light conversion material 4240. However this is not alimitation of the present invention and in other embodiments lightconversion material 4240 may cover only a portion of LED units 4220, ormay cover only portions of each LED unit 4220. In some embodiments ofthe present invention wherein substrate 4210 comprises a transparentsubstrate, light conversion material 4240 may be formed over the side ofsubstrate 4210 opposite LED units 4220.

Bottom confining region 4260, top confining region 4268 and/or activeregion 4264 may each comprise one or more layers. Bottom confiningregion 4260 and top confining region 4268 may have a bandgap relativelylarger than that of all or a portion of active region 4264 or of the oneor more layers comprising active region 4264. In some embodiments of thepresent invention active region 4264 may comprise one or more quantumwells and barriers. In some embodiments of the present invention activeregion 4264 may comprise one or more layers of quantum dots, or quantumwires and barriers. As is well understood by those familiar with theart, additional layers may be present and this invention is not limitedin this regard. Furthermore, the layers comprising bottom confiningregion 4260, top confining region 4268 and active region 4264 may becomprised of a wide range of materials, depending on the desiredproperties, and in particular, the emission wavelength, of the LED.

In one example in which the LED may emit UV, blue or green light,substrate 4210 may comprise sapphire, bottom confining region 4260,active region 4264 and top confining region 4268 may compriseAlxInyGa1-x-yN, with x and y adjusted in each layer such that thebandgap of bottom confining region 4260 and top confining region 4268are larger than the bandgap of the light emitting layer in active region4264. In some embodiments of this example bottom confining region 4260may be doped n-type and top confining region 4268 may be doped p-type.However, this is not a limitation of the present invention and in otherembodiments bottom confining region 4260, top confining region 4268 andactive region 4264 may comprise other materials and have otherconductivity types.

FIG. 45 is a cross-sectional view of structure 500 in accordance withanother embodiment of the present invention. The semiconductor structurein FIG. 45 may be referred to as a monolithically formed light system orlight engine. FIG. 46 is a view of the structure of FIG. 45 from thelight emitting side of structure 500, that is side of carrier 1510 overwhich LED units 110 may be formed and FIG. 44 is a cross-sectional viewtaken along section line 45-45 of FIG. 46. In FIG. 45 optional lightconversion material 1810 is not shown, and opening 5310 and 5320 areshown as dotted lines to indicate that they are under layer 5410.

The monolithic light engine shown schematically in FIG. 45 comprises acarrier 1510, a plurality of LED units 110, layers 1520, 4610 and 4520used to attach LED units 110 to carrier 1510, optional light conversionmaterial 1810, a layer 5210, a layer 5410 and contact regions 120A and120B. Carrier 1510 may be referred to as a carrier, a substrate, amechanical support, a heat sink or a first level heat sink. Layers 1520and 4520 may be used to help attach LED units 110 to carrier 1510. LEDunit 110 may comprise a bottom confining region 220, an active region230, a top confining region 240, a portion of layer 5410, a portion oflayer 5210 and a portion of top contact layer 4510.

Light is generated in active region 230 and exits LED unit 110 throughopening 5320A. In some embodiments of the present invention lightextraction features 5010 may be formed in or on a portion of LED unit110 to improve the light extraction efficiency. In some embodiments ofthe present invention, light extraction features may comprise one ormore anti-reflection coatings and/or surface roughening, texturing,patterning, imprinting or the like. In some examples such lightextraction features may be formed in a regular periodic array, howeverthis is not a limitation of the present invention and in otherembodiments, light extraction features may be formed in a random orsemi-random pattern.

Some of the light generated in active region 230 may exit the activeregion into top confining region 240. Such light may be reflected fromreflecting surfaces that reflect a wavelength of light emitted by theLED that are formed over portions of or all of top confining region 240,for example on the side of top confining region 240 adjacent to carrier1510. In some embodiments of the present invention reflecting surfacesmay also be formed over portions of or all of active region 230 andbottom confining region 220, in particular on all or a portion of thesidewalls of active region 230 and bottom confining region 220. In someembodiments of the present invention, such reflecting surfaces may havea reflectivity greater than 80% to a wavelength of light emitted by theLED, or greater than 90% to a wavelength of light emitted by the LED, orgreater than 95% to a wavelength of light generated in active region230.

Optional light conversion material 1810 may comprise organic orinorganic phosphors or other materials capable of absorption of aportion of the light emitted from active region 230 and re-emitting itat a different wavelength. In some embodiments of the present inventionlight conversion material 1810 may comprise a down conversion materialand in other embodiments light conversion material 1810 may comprise anup conversion material. In some embodiments of the present invention,optional light conversion material 1810 may be suspended or embedded ina second material (not shown), and in some embodiments the secondmaterial may comprise a material with an index of refraction betweenthat of the material in layer structure 250 (FIG. 20) and air. In oneexample of this embodiment such second material may comprise for examplean epoxy, gel, or resin with an index of refraction in the range ofabout 1.2 to about 1.7. Such a second material may act to reduce totalinternal reflection and increase the light extraction efficiency of thelight engine.

LED unit 110 may be formed such that the heat-generating active region230 may be in close proximity to carrier/heat sink 1510, for example allor a portion of active region 230 may be spaced less than 10 μm, or maybe less than 5 μm, or may be less than 2 μm from the surface of carrier1510 adjacent to attachment layer 1520. In other words, the combinedthickness of layer 4610, 1520, 4520, 4510 and top confining region 240may be less than 10 μm, or may be less than 5 μm, or may be less than 2μm.

Referring now to FIG. 46, FIG. 46 shows a top view example ofsemiconductor structure 500 comprising four (4) LED units 110. In FIG.46 optional light conversion material 1810 is not shown, and opening5310 and 5320 are shown as dotted lines to indicate that they are underlayer 5410, as discussed above. In this example the LEDs are configuredas shown in FIG. 10A, comprising two parallel strings of LEDs, eachstring of LEDs comprising two LED units 110. In this example electricalconnection to the positive polarity terminal of the light engine may bemade through contact region 120A, which comprises a portion of layer5410 that may be coupled to the top confining region 240 of LED units110 A and B through top contact layer 4510. Similarly, electricalconnection to the negative polarity terminal of the light engine may bemade through contact region 120B, which comprises a portion of layer5410 that may be coupled to bottom confining region 220 of LED units Cand D. Bottom confining region 220 of LED units A and B may beelectrically coupled to top confining region 240 of LED units C and Drespectively through a portion of layer 5410.

In the example shown in FIG. 46, LED units 110 are configured as shownschematically in FIG. 10A. However this is not a limitation of thepresent invention and in other embodiments LED units may be connected inany other configuration; the connection topology is not a limitation ofthe present invention. For example, in some embodiments of the presentinvention, the individual LED units may be coupled in series as shown inFIG. 10C, in parallel as shown in FIG. 10B or a combination of seriesand parallel connections as shown in FIG. 10D. In some embodiments, aportion or all of the individual LED units 110 may be coupled anode tocathode as shown in FIGS. 10A to 10D while in other embodiments contactregions 120A and 120B may each have both one or more anodes and one ormore cathodes of individual LED units 110 coupled to them as shown inFIG. 10E, and in other embodiments, a combination of these types ofcouplings may be utilized.

FIGS. 45 and 46 show an exemplary LED array with 4 LED units 110.However, the number of LED units 110 is not a limitation of the presentinvention and in some embodiments the LED array may comprise a largernumbers of LED units 110. In some embodiments of the present inventionthe number of LED units 110 in the array may be greater than 20, or maybe greater than 50, or may be greater than 100 or may be greater than250 or may be greater than 500.

FIG. 20 is a cross-sectional view of a semiconductor structure at abeginning stage of manufacture that may be used as a starting structurefor the semiconductor structure of FIG. 45, in accordance with anembodiment of the present invention. FIG. 20 comprises substrate 210,bottom confining region 220 that may be formed over substrate 210,active region 230 that may be formed over bottom confining region 220and top confining region 240 that may be formed over active region 230.

Substrate 210 may comprise a semiconductor material such as, forexample, gallium arsenide (GaAs), gallium phosphide (GaP), indiumphosphide (InP), sapphire, silicon carbide (SiC), aluminum nitride(AlN), ZnO, diamond, silicon or other semiconductors, and may be dopedor undoped depending on the application, although the methods andapparatuses described herein are not limited in this regard. In otherembodiments of the present invention, substrate 210 may comprise othermaterials such as, for example, glass, polymers or metals. Substrate 210may have a thickness ranging from about 50 μm to about 2,000 μm, butthis is not a limitation of the present invention and in otherembodiments the substrate may have any thickness. The thickness ofsubstrate 210 may be reduced through subsequent thinning processes insome embodiments. In some embodiments a portion or all of substrate 210may be ultimately removed from the final structure. In some embodimentssubstrate 210 may comprise more than one material, for example a layerof one material formed over a second material. In one example such asubstrate may comprise a zinc oxide layer (ZnO) layer formed over anon-crystalline substrate. Substrate 210 may be absorbing to orsubstantially transparent, or translucent at a wavelength of lightgenerated by the light-emitting device.

Substrate 210 may have a diameter in the range of about 1″ to more thanabout 12″, however the diameter of substrate 210 is not a limitation ofthe present invention and in other embodiments substrate 210 may haveany diameter. It may be desirable for substrate 210 to have a relativelylarge diameter, as this permits a larger number of LED arrays or lightengines to be fabricated in a batch mode on a single substrate (at thewafer level). In some embodiments of the present invention substrate 210may have a circular shape, like that often used for conventionalsemiconductor processing. However this is not a limitation of thepresent invention and in other embodiments substrate 210 may be square,rectangular or have any arbitrary shape.

In some embodiments bottom confining region 220 may be doped n-type andtop confining region 240 may be doped p-type, but this is not alimitation of the present invention and in other embodiments each layermay be either n-type, p-type or undoped. In some embodiments bottomconfining region 220 may have a thickness in the range of about 0.5 μmto about 10 μm. In some embodiments active region 230 may have athickness in the range of about 5 angstrom (Å) to about 10,000 Å. Insome embodiments top confining region 240 may have a thickness in therange of about 0.05 μm to about 5 μm. Together bottom confining region220, active region 230 and top confining region 240 may be referred toas layer structure 250. In some embodiments of the present invention LEDunit 110 may comprise a plurality of active regions 230 betweenconfining layers 220 and 240. In some embodiments of the presentinvention, these separate active regions may emit at the same ordifferent wavelengths.

In some embodiments of the present invention it may be desirable tominimize the thickness of layer structure 250. For example in someembodiments of the present invention, portions of layer structure 250may be removed, resulting in steps in layer structure 250 and minimizingthe thickness of layer structure 250 may simplify the processing steps,for example removal of portions of layer structure 250 and metallizationover said steps, by reducing said step or steps height.

The structure shown in FIG. 20 comprises the layer structure 250 formedover substrate 210 and may be referred to as an LED epi wafer. Bottomconfining region 220, top confining region 240 and/or active region 230may each comprise one or more layers. Bottom confining region 220 andtop confining region 240 may have a bandgap relatively larger than thatof all or a portion of active region 230 or of the one or more layerscomprising active region 230. In some embodiments of the presentinvention active region 230 may comprise one or more quantum wells andbarriers. In some embodiments of the present invention active region 230may comprise one or more layers of quantum dots, or quantum wires andbarriers. As is well understood by those familiar with the art,additional layers may be present and this invention is not limited inthis regard. Furthermore, the layers comprising layer structure 250 maybe comprised of a wide range of materials, depending on the desiredproperties, and in particular, the emission wavelength of the LED.

In some embodiments of the present invention top confining region 240may comprise a Distributed Bragg Reflector (DBR) (not shown) which mayact as a mirror to light of a wavelength emitted by active region 230.In some embodiments of the present invention the DBR (not shown) mayhave a reflectivity of higher than about 70%, or higher than about 80%,or higher than about 90% to light of a wavelength emitted by activeregion 230 perpendicularly incident upon said DBR. In other embodimentsof the present invention a DBR (not shown) may be formed over topconfining region 240 or between top confining region 240 and activeregion 230.

In some embodiments of the present invention layer structure 250 maycomprise epitaxial layers and be formed using techniques such as metalorganic vapor phase epitaxy (MOVPE), molecular beam epitaxy (MBE),hydride vapor phase epitaxy (HVPE), liquid phase epitaxy (LPE), chemicalvapor deposition (CVD) or the like. In some embodiments of the presentinvention layer structure 250 may comprise polycrystalline or amorphouslayers and be formed using techniques such as chemical vapor deposition(CVD), evaporation, sputtering or the like. However this is not alimitation of the present invention and in other embodiments layerstructure 250 may be formed by any means and may be single crystal,polycrystalline or amorphous.

In one example, in which the LED may emit red/orange/yellow light,substrate 210 may comprise GaAs, bottom confining region 220, activeregion 230 and top confining region 240 may comprise AlxInyGa1-x-yP,with x and y adjusted in each layer such that the bandgap of bottomconfining region 220 and top confining region 240 are larger than thebandgap of the light emitting layer in active region 230. In someembodiments of this example substrate 210 may be doped n-type, bottomconfining region 220 may be doped n-type and top confining region 240may be doped p-type.

In another example, in which the LED may emit UV, blue or green light,substrate 210 may comprise sapphire, bottom confining region 220, activeregion 230 and top confining region 240 may comprise AlxInyGa1-x-yN,with x and y adjusted in each layer such that the bandgap of bottomconfining region 220 and top confining region 240 are larger than thebandgap of the light emitting layer in active region 230. In someembodiments of this example substrate 210 may be doped n-type, bottomconfining region 220 may be doped n-type and top confining region 240may be doped p-type.

In another example, in which the LED may emit UV, blue or green light,substrate 210 may comprise Si, SiC, AlN, ZnO, diamond, glass or apolymer, bottom confining region 220, active region 230 and topconfining region 240 may comprise AlxInyGa1-x-yN, with x and y adjustedin each layer such that the bandgap of bottom confining region 220 andtop confining region 240 are larger than the bandgap of the lightemitting layer in active region 230. In some embodiments of this examplesubstrate 210 may be doped n-type, bottom confining region 220 may bedoped n-type and top confining region 240 may be doped p-type.

In some embodiments of the present invention layer structure 250 maycomprise one or more buffer layers (not shown in FIG. 20) formed betweenbottom confining region 220 and substrate 210, the purpose of which isto improve the quality of the subsequently formed bottom confiningregion 220, active region 230 and top confining region 240. In oneexample, in which the LED may emit UV, blue or green light and substrate210 comprises sapphire, additional buffer layers may comprise a lowtemperature GaN or AlxGa1-xN layer and a doped GaN layer. In someembodiments of this aspect of the present invention, layer structure 250may further comprise an insulating layer (not shown) formed over aportion of the layers within layer structure 250 but below active region230. Said insulating layer may result in process simplification becausesubsequent isolation of the individual LED units 110 by removal of aportion of layer structure 250 may only need to be done down to theoptional insulating layer, thus reducing the step height in one or moresteps formed in layer structure 250. Said insulating layer may comprise,for example, AlN or AlxGa1-xN, however this is not a limitation of thepresent invention and in other embodiments said insulating layer maycomprise any material.

FIG. 47 is a cross-sectional view of the structure of FIG. 20 at a laterstage of manufacture. After formation of layer structure 250 (FIG. 20),top contact 4510 may be formed over top confining region 220 andattachment layer 4520 may be formed over top contact 4510 using wellknown semiconductor processes. Top contact 4510 may also be referred toas a top electrical contact. For example, in some embodiments, topelectrical contact 4510 and attachment layer 4520 may be formed using alift-off process in which the semiconductor structure of FIG. 20 ispatterned using photolithography, the material comprising top electricalcontact 4510 is formed over the photoresist (not shown) and the portionsof top confining region 240 exposed by openings in said photoresist (notshown), the material comprising attachment layer 4520 is formed over thematerial forming top electrical contact 4510, removing the photoresistalong with the material comprising top electrical contact 4510 andattachment layer 4520 formed over the photoresist, leaving attachmentlayer 4520 formed over top contact material 4510 only in open regions(not covered by photoresist), thus forming attachment layer 4520 overtop electrical contact 4510, which is formed over top confining layer240 as shown in FIG. 47.

In another example, the material comprising top electrical contact 4510may be formed over the entire semiconductor structure shown in FIG. 20,the material comprising attachment layer 4520 may be formed over thematerial comprising top electrical contact 4510, patterning the materialcomprising attachment layer 4520 and the material comprising underlyingtop electrical contact 4510 using photolithography with a pattern thatleaves attachment layer 4520 covered with photoresist, removing theexposed material comprising attachment layer 4520 and the materialcomprising top electrical contact layer 4510, and removing the remainingresist, thus forming attachment layer 4520 over top electrical contact4510, as shown in FIG. 47. These examples are meant to be illustrativeand other techniques for formation of the structure of FIG. 47 may beused as well.

In FIG. 47 attachment layer 4520 is shown as the same size as topcontact 4510. However this is not a limitation of the present inventionand in other embodiments attachment layer 4520 may be smaller than topcontact 4510. In some embodiments of the present invention attachmentlayer 4520 may be smaller than top contact 4510 to prevent shorting ofadjacent LED units 110 if the attachment material flows beyond thedimensions of top contact 4510 and, for example, contacts an adjacentLED unit 110.

Top electrical contact 4510 may comprise one or more layers. Topelectrical contact 4510 may comprise metals, silicides or otherconductive materials. The specific material(s) used for top electricalcontact 4510 will depend on the specific semiconductors in layerstructure 250 (FIG. 20). For example, in the case where layer structure250 (FIG. 20) may comprise GaAs- or GaP-based semiconductors, topelectrical contact 4510 may comprise Au, Au/Ge or Au/Ge/Ni. In theexample where layer structure 250 (FIG. 20) may comprise GaN-basedsemiconductors, top electrical contact 4510 may comprise Ni/Au. In someembodiments the thickness of top electrical contact 4510 may be in therange of about 100 Å to about 5000 Å, but this is not a limitation ofthe present invention and in other embodiments contact material 4510 maybe any thickness. In some embodiments of the present invention topelectrical contact 4510 may be formed using techniques such asevaporation, sputtering, chemical vapor deposition (CVD), low pressurechemical vapor deposition (LPCVD), oxidation, spin deposition or thelike.

In some embodiments of the present invention, one or more heattreatments may be required to achieve acceptable ohmic contact betweentop electrical contact 4510 and top confining region 240 and betweeninterconnect layer 5410 (FIG. 45) and bottom confining region 220.Acceptable ohmic contact may mean a specific contact resistance of lessthan 1E-3 Ω-cm2, or less than 1E-4 Ω-cm2. Such heat treatments may beperformed, for example, in a furnace, on a hot plate, in a rapid thermalanneal system or the like. Annealing temperatures may range from about300° C. to about 800° C., however the method and time and temperature ofthe anneal are not limitations of the present invention and in otherembodiments, other annealing methods, temperatures or temperatureprofiles, or times may be used. In some embodiments of the presentinvention, the anneal for top electrical contact 4510 may be performedprior to the formation of interconnect layer 5410. In other embodimentsof the present invention, top electrical contact 4510 may be formed andannealed before formation and anneal of the bottom contact to bottomconfining region 220. In all cases, it is important to note that thefirst-formed contact will also receive the anneal process from thesecond-formed contact. In some embodiments of the present invention, oneanneal step may be carried out after formation of both the bottomelectrical contact and top electrical contact 4510. Annealing may bedone in an inert ambient, for example nitrogen, a reducing ambient, forexample forming gas, or any other ambient; the annealing ambient is nota limitation of the present invention.

In some embodiments of the present invention, it may be desirable tominimize the annealing temperature and/or time or to eliminate theannealing altogether, for example when top contact 4510 and/or bottomcontact to bottom confining region 220 also act as a mirror (discussedbelow). In this example, reduced annealing temperatures and/orelimination of the annealing step or steps altogether may provide ahigher reflectivity to a wavelength of light emitted by thelight-emitting device.

Attachment layer 4520 may be used to attach the semiconductor structureof FIG. 47 to carrier 1510 (FIG. 48) in conjunction with attachmentlayer 1520. In one example attachment layer 4520 may comprise a solder,for example an Au/Sn solder, an In solder or an In/Sn solder. The numberof elements in the solder and the composition of the solder are not alimitation of the present invention and in other embodiments, attachmentlayer 4520 may comprise any type of solder or composition of solder. Inother embodiments of the present invention, attachment layer 4520 maycomprise a glue or adhesive; the type of glue or adhesive is not alimitation of the present invention and in other embodiments attachmentlayer 4520 may comprise any type of glue or adhesive. In the examplewhere attachment layer 4520 may comprise a solder, for example an Au/Snsolder, attachment layer 1520 may comprise a layer to which a solder mayform a suitable bond, for example a metal such as Au, Sn, or othermetals. In some embodiments of the present invention attachment layer4520 and/or attachment layer 1520 may be formed using, for example,evaporation, plating, sputtering, CVD, LPCVD, screen printing,dispensing or other techniques. In some embodiments of the presentinvention attachment layer 4520 and/or attachment layer 1520 may eachhave a thickness in the range of about 5 nm to about 5 μm. In someembodiments of the present invention attachment layer 4520 and/orattachment layer 1520 may each have a thickness in the range of about0.25 μm to about 3 μm.

In some embodiments of the present invention, attachment layer 4520and/or attachment layer 1520 may have a relatively high thermalconductivity and may provide a pathway for heat removal from activeregions 230 of LED units 110. In some embodiments of the presentinvention attachment layer 4520 and/or attachment layer 1520 may have athermal conductivity higher than 0.5 W/cm-K, or higher than 1 W/cm-K. Insome embodiments of the present invention, attachment layer 4520 and/orattachment layer 1520 may have a relatively high resistivity, forexample higher than 1E4 Ω-cm, or higher than 1E5 Ω-cm, or higher than1E6 Ω-cm, however this is not a limitation of the present invention andin other embodiments attachment layer 4520 and/or attachment layer 1520may be semiconducting or conductive.

In some embodiments of the present invention, attachment layer 4520and/or attachment layer 1520 may each comprise a plurality of layers. Insome embodiments of the present invention, only one attachment layer maybe utilized and this may be formed over the semiconductor structure ofFIG. 47 or over carrier 1510 (FIG. 48).

After the deposition of attachment layer 4520 and/or attachment layer1520 and prior to the attachment of the semiconductor structure of FIG.47 to carrier 1510 (FIG. 48), attachment layer 4520 (FIG. 47) and/orattachment layer 1520 (FIG. 48) may be polished or planarized using, forexample, chemical mechanical polishing (CMP), to form a relatively highquality bond during the attachment step.

Referring now to FIG. 48, FIG. 48 is a cross-sectional view of carrier1510 comprising optional insulating layer 4610 formed over carrier 1510and attachment layer 1520 formed over optional insulating layer 4610.Carrier 1510 may comprise an insulator, a semiconductor or a conductor.Carrier 1510 may comprise, for example a semiconductor such as AlN, SiC,silicon, polysilicon, GaAs, GaP, InP, sapphire, diamond or othersemiconductors and may be doped or undoped depending on the application,although the methods and apparatuses described herein are not limited inthis regard. In other embodiments of the present invention, carrier 1510may comprise other materials such as, for example, glass, polymers ormetals. Carrier 1510 may have a thickness ranging from about 50 μm toabout 2,000 μm, but this is not a limitation of the present inventionand in other embodiments the substrate may have any thickness. Thethickness of carrier 1510 may be reduced through subsequent thinningprocesses in some embodiments. In some embodiments of the presentinvention carrier 1510 may comprise more than one material, for examplea layer of a first material formed over a second material. Carrier 1510may be absorbing to or substantially transparent at a wavelength oflight generated by the light-emitting device.

Carrier 1510 may have a diameter in the range of about 1″ to over 12″,however the diameter of carrier 1510 is not a limitation of the presentinvention and in other embodiments carrier 1510 may have any diameter.It may be desirable for carrier 1510 to have a diameter the same as, orsubstantially the same as substrate 210 (FIG. 47) however this is not alimitation of the present invention and in other embodiments, carrier1510 may have a diameter larger than or smaller than the diameter ofsubstrate 210 (FIG. 47).

In some embodiments of the present invention carrier 1510 may have acircular shape, like that often used for conventional semiconductorprocessing. However this is not a limitation of the present inventionand in other embodiments carrier 1510 may be square, rectangular or haveany arbitrary shape. In some embodiments of the present invention theshape and size of carrier 1510 may be the same as, or substantially thesame as that of substrate 210 (FIG. 47). However this is not alimitation of the present invention and in other embodiments carrier1510 and substrate 210 may have different shapes and sizes.

In some embodiments of the present invention, carrier 1510 may have arelatively high thermal conductivity and may provide a pathway for heatremoval from active regions 230 of LED units 110. In some embodiments ofthe present invention carrier 1510 may have a thermal conductivityhigher than 0.15 W/cm-K, or higher than 0.5 W/cm-K, or higher than 1W/cm-K. In some embodiments of the present invention, carrier 1510 mayhave a relatively high resistivity, for example greater than 1E4 Ω-cm,or greater than 1E5 Ω-cm, or greater than 1E6 Ω-cm, however this is nota limitation of the present invention and in other embodiments carrier1510 may be semiconducting or conductive.

Attachment layer 1520 may comprise a material compatible with and usedin conjunction with attachment layer 4520 to join attachment layer 4520to attachment layer 1520. For example, in the example where attachmentlayer 4520 may comprise a solder, for example a Au/Sn solder, attachmentlayer 1520 may comprise a layer to which a solder may form a suitablebond, for example a metal such as Au, Sn, or other metals. In someembodiments of the present invention attachment layer 1520 may be formedusing, for example, evaporation, plating, sputtering, CVD, LPCVD, screenprinting, dispensing or other techniques. In some embodiments of thepresent invention attachment layer 1520 may have a thickness in therange of about 50 nm to about 5 μm. In some embodiments of the presentinvention attachment layer 1520 may have a thickness in the range ofabout 0.25 μm to about 3 μm.

In some embodiments of the present invention attachment layer 1520 maybe patterned using standard processing techniques as shown in FIG. 48.Patterning may be used to electrically isolate each LED unit 110 fromthe other LED units 110 in the case where attachment layer 1520 may beelectrically conductive. If attachment layer 1520 is not electricallyconductive, or if top electrical contact 4510 of each LED unit 110 iselectrically isolated from all other top electrical contacts 4510 of theother LED units 110, attachment layer 1520 may not need to be patterned.In some embodiments of the present invention attachment layer 1520and/or attachment layer 4510 may be patterned and provide electricalcoupling between all or a portion of LED units comprising the lightengine.

Optional insulating layer 4610 may comprise, for example, silicondioxide, silicon nitride, sapphire, high resistivity polysilicon,aluminum nitride, silicon carbide or the like. Optional insulating layer4610 may be used to provide electrical isolation between attachmentlayer 1520 and carrier 1510, or between top contact 4510 and carrier1510. In some embodiments of the present invention, optional insulatinglayer 4610 may be used in conjunction with carrier 1510 that iselectrically conductive. In some embodiments of the present inventioninsulating layer 4610 may be formed using, for example, oxidation,evaporation, plating, sputtering, CVD, LPCVD, screen printing, spindeposition, dispensing or other techniques. In some embodiments of thepresent invention carrier 1510 may comprise silicon and insulating layer4610 may comprise silicon dioxide formed by oxidation of a portion ofthe surface of carrier 1510. In some embodiments of the presentinvention insulating layer 4610 may have a thickness in the range ofabout 2 nm to about 5 μm. In some embodiments of the present inventioninsulting layer 4610 may have a thickness in the range of about 0.05 μmto about 0.5 μm. However the thickness of insulating layer 4610 is not alimitation of the present invention and in other embodiments, insulatinglayer 4610 may have any thickness or be formed by any means.

In the example shown in FIG. 48 optional insulating layer 4610 is shownas covering the entire surface of carrier 1510. However, this is not alimitation of the present invention and in other embodiments of thepresent invention, optional insulating layer 4610 may cover onlyportions of carrier 1510. In some embodiments of the present invention,attachment layer 1520 may act as an electrical conductor and provide oneor more pathways for power and/or signals to LED units 110.

In some embodiments of the present invention, attachment layer 4520(FIG. 47) and/or optional insulating layer 4610 and/or attachment layer1520 may have a relatively high thermal conductivity and may provide apathway for heat removal from active regions 230 of LED units 110. Insome embodiments of the present invention attachment layer 4520 (FIG.47) and/or optional insulating layer 4610 and/or attachment layer 1520may have a thermal conductivity higher than 0.5 W/cm-K, or higher than 1W/cm-K. In some embodiments of the present invention, attachment layer4520 (FIG. 47) and/or optional insulating layer 4610 and/or attachmentlayer 1520 may have a relatively high resistivity, for example higherthan 1E4 Ω-cm, or higher than 1E5 Ω-cm, or higher than 1E6 Ω-cm, howeverthis is not a limitation of the present invention and in otherembodiments attachment layer 4520 (FIG. 47) and/or optional insulatinglayer 4610 and/or attachment layer 1520 may be semiconducting orconductive.

In some embodiments of the present invention, attachment layer 4520(FIG. 47) and/or optional insulating layer 4610 and/or attachment layer1520 may each comprise a plurality of layers. In some embodiments of thepresent invention, only one attachment layer may be utilized and thismay be formed over either the semiconductor structure of FIG. 47 or overcarrier 1510 (FIG. 48). In the example shown in FIGS. 47 and 48,attachment layer 4520 comprised a solder, glue adhesive or other likematerials and attachment layer 1520 comprised a material compatible withand to be used in conjunction with attachment layer 4520, however thisis not a limitation of the present invention and in other embodiments,the roles of attachment layers 1520 and 4520 may be reversed.

After the formation of attachment layer 1520 (FIG. 48) and/or attachmentlayer 4520 (FIG. 47) and prior to the attachment or mating of theselayers, attachment layer 4520 (FIG. 47) and/or attachment layer 1520(FIG. 48) may be polished or planarized using, for example, chemicalmechanical polishing (CMP), to form a relatively high quality bondduring the attachment step.

FIG. 49 is a cross-sectional view of the semiconductor structure of FIG.47 at a later stage of manufacture. After formation of attachment layer4520 (FIG. 47) and formation of attachment layer 1520 (FIG. 48), surface4655 of the semiconductor structure of FIG. 47 and surface 1530 of thecarrier of FIG. 48 may be joined or attached, as shown in FIG. 49. Themethod of joining depends on the materials used for attachment layers4520 and 1520. In some embodiments, the joining may be performed usingthermocompression bonding, wafer bonding, adhesive, glue, solder or thelike. In the example where attachment layer 4520 comprises an Au/Snsolder and attachment layer 1520 comprises Au, joining may beaccomplished using a combination of heat and pressure, in other wordsusing thermocompression bonding. In the case where attachment layer 4520and/or attachment layer 1510 comprise a glue or adhesive, joining may beaccomplished by mating surface 4655 (FIG. 47) and surface 1530 (FIG. 48)and the optional application of pressure and/or heat.

FIG. 50 is a cross-sectional view of the semiconductor structure of FIG.49 at a later stage of manufacture. After joining surface 4655 of thesemiconductor structure of FIG. 47 and surface 1530 of the carrier ofFIG. 48, a portion or all of substrate 210 may be optionally removed. Inthe example shown in FIG. 50, all of substrate 210 is removed. Substrate210 may be removed using techniques such as lapping and polishing, CMP,wet chemical etching, reactive ion etching (RIE), laser lift-off or thelike. In some embodiments of the present invention, removal of substrate210 may comprise more than one step.

FIG. 51 is a cross-sectional view of the semiconductor structure of FIG.50 at a later stage of manufacture. After removal of substrate 210, aportion of bottom confining region 220 may be optionally removed. Aportion of bottom confining region 220 may be removed using techniquessuch as lapping and polishing, CMP, wet chemical etching, reactive ionetching (RIE) or the like. In some embodiments of the present invention,removal of a portion of bottom confining region 220 may comprise morethan one step.

In some embodiments of the present invention the amount of bottomconfining region 220 remaining after removal may be in the range ofabout 0.05 μm to about 2 μm, however this is not a limitation of thepresent invention and in other embodiments any amount of bottomconfining region may be left remaining, including all of bottomconfining region 220 or none of bottom confining region 220. In someembodiments of the present invention it may be desirable to optimize theamount of bottom confining region 220 remaining with respect to currentspreading, process simplification and light absorption. Currentspreading may be improved with a relatively thicker remaining bottomconfining region 220. However, processing may be easier because of theease of photolithography and metallization and general processing overregions with relatively smaller step heights and light absorption may beless with a relatively thinner remaining bottom confining region 220.

In some embodiments of the present invention layer structure 250 (FIG.20) may comprise an etch stop layer having a high selectivity to removalor etching compared to the material comprising bottom confining region220. Such an etch stop layer may act as an aide to controlling thethickness of the remaining portion of bottom confining region 220 duringthe previous steps. In some embodiments of the present invention saidetch stop layer may be formed between bottom confining region 220 andsubstrate 210, however this is not a limitation of the present inventionand in other embodiments said etch stop layer may be formed withinbottom confining region 220 or anywhere within layer structure 250 (FIG.20).

In some embodiments of the present invention characteristics of the etchprocess, for example the spectral characteristics of the gas in a RIEtype etch process, or the chemical constituents of the removal process,for example dry or wet etching, may be used as a marker to determinewhen to terminate the removal process of portions or all of bottomconfining region 220. In some embodiments of the present invention layerstructure 250 (FIG. 20) may comprise a marker layer for said purpose. Insome embodiments of the present invention said marker layer may beformed between bottom confining region 220 and substrate 210, howeverthis is not a limitation of the present invention and in otherembodiments said marker layer may be formed within bottom confiningregion 220 or anywhere within layer structure 250 (FIG. 20).

FIG. 52 is a cross-sectional view of the semiconductor structure of FIG.51 at a later stage of manufacture. After optional removal of a portionof bottom confining region 220, light extraction features 5010 may beformed in all or a portion of or on the surface of bottom confiningregion 220, and/or optionally in all or portions of active region 230and top confining region 240 to improve the light extraction efficiency.In some embodiments of the present invention, light extraction features5010 may comprise one or more anti-reflection coatings and/or surfaceroughening, texturing, patterning, imprinting or the like. In someexamples light extraction features 5010 may be formed in a regularperiodic array, however this is not a limitation of the presentinvention and in other embodiments, light extraction features 5010 maybe formed in a random or semi-random pattern.

FIG. 53 is a cross-sectional view of the semiconductor structure of FIG.52 at a later stage of manufacture. After formation of light extractionfeatures layer 5110 may be optionally formed over bottom confiningregion 220 and light extraction features 5010. Layer 5110 may comprise aconductive coating that is relatively transparent to a wavelength oflight emitted by LED unit 110. Layer 5110 may act to improve currentspreading in and across bottom confining region 220. Interconnect 5410(FIG. 44) may make contact with the layer 5010 and bottom confiningregion 220 at the periphery of region 5320A (FIG. 44). The addition oflayer 5110 may relatively improve the spread of current through bottomconfining region 220 and active region 230, thus providing more evenlight generation across region 5320A (FIG. 44) and an improved LEDluminous efficacy.

Layer 5110 may comprise a transparent conductive oxide, for exampleindium tin oxide (ITO), ZnO, AlN, SiC, conductive polymers, carbonnanotubes, thin metal layers or the like. In some embodiments of thepresent invention, layer 5110 may comprise a relatively thin layer ofmetal, such that the transparency of the metal is relatively high. Sucha metal may comprise, for example, Au, Ni, Cr, Ru, or Rh. The thicknessof such a metal layer may be in the range of about 0.1 nm to about 10nm. The material comprising layer 5110 is not a limitation of thepresent invention.

FIG. 54 is a cross-sectional view of the semiconductor structure of FIG.53 at a later stage of manufacture. After formation of layer 5110, layer5110 and light extraction features 5010, layer structure 250 may bepatterned using photolithography and etching processes to form one ormore mesas 410. In some embodiments of the present invention layer 4510,layer 4520 and layer 1520 may also be patterned during this step. Anisotropic or anisotropic etch process such as, for example, wet chemicaletching or a reactive ion etch (“RIE”), may be used to form one or moremesas 410. In some embodiments, mesa 410 may be formed in one etchprocess or step, however this is not a limitation of the presentinvention and in other embodiments more than one etch process or stepmay be used to form mesa 410.

In some embodiments one or more hard mask layer(s) (not shown) may beformed over layer 5110 before patterning. Since the photoresist overlayer 5110 is also etched as part of the etch used to etch portions oflayer 5110, light extraction features 5010 and layer structure 250, ahard mask layer or layers may be used to prevent the undesired etchingof the upper surface of layer 5110 during the formation of mesa 410. Oneor more hard mask layers are optional, and in alternate embodiments, thephotoresist layer may be made relatively thick such that it is notcompletely eroded during the formation process of mesa 410, andtherefore, the photoresist may be used as a masking layer rather thanusing a hard mask layer. A hard mask layer may comprise, for example, adielectric such as silicon dioxide (“SiO2”) or silicon nitride(“Si3N4”), or a metal, such as nickel, titanium, aluminum, gold,chromium or the like.

Mesas 410 form LED units 110 as identified in FIG. 45. Referring to FIG.46, LED units 110 are shown as having a square shape, however this isnot a limitation of the present invention and in other embodiments LEDunit 110, and thus mesa 410 may be rectangular, hexagonal, circular orany arbitrary shape. FIG. 46 shows all LED units 110 having the sameshape, however this is not a limitation of the present invention and inother embodiments a plurality of shapes for LED units 110, and thus mesa410, may be employed. FIG. 46 shows each LED unit 110 being spaced apartfrom adjacent LED units 110 an equal distance. However, this is not alimitation of the present invention and in other embodiments the spacingbetween LED units 110 and thus mesas 410 may not be equal.

Mesas 410 have a top surface 440. In one example, mesa 410 may comprisea square and top surface 440 may have a length in the range of about 75μm to about 1000 μm. In another embodiment mesa 410 may comprise asquare and top surface 440 may have a length in the range of about 200μm to about 500 μm. In some embodiments the spacing between mesas 410may be uniform and be in the range of about 15 μm to about 10,000 μm. Inanother embodiment the spacing between mesas 410 may be uniform and bein the range of about 25 μm to about 200 μm.

In the example shown in FIG. 54, the etch depth (or the height of mesa410) is equal to the thickness of layer structure 250 plus the thicknessof layer 5110 and light extraction features 5010. In other words, all oflayer structure 250 (FIG. 20) is removed outside of the region of mesa410. However this is not a limitation of the present invention and inother embodiments, the etch depth may be less than that of the thicknessof layer structure 250, in other words leaving all or a portion of topconfining region 240 and/or all or a portion of active region 230.

The sidewalls 420 of mesa 410 may be sloped as shown in FIG. 54 and havea slope in the range of about 20 degrees to about 75 degrees. Howeverthis is not a limitation of the present invention and in otherembodiments sidewalls 420 of mesa 410 may have any angle with respect tosurface 440, including perpendicular or substantially perpendicular tosurface 440.

After formation of mesa 410, layer 5210 may be formed over mesa 410, aportion of top contact 4510, a portion of attachment layer 4520, layer1520 and a portion of layer 4610. Layer 5210 may comprise an insulatinglayer and may provide electrical isolation between mesa 410, a portionof top contact 4510 and a portion of attachment layer 4520 and/or 1520and the subsequently formed overlying interconnect layer 5410 (FIG. 45).Layer 5210 may comprise, for example, silicon dioxide, silicon nitride,sapphire, high resistivity polysilicon, aluminum nitride, siliconcarbide or the like. In some embodiments of the present invention layer5210 may be formed using, for example, evaporation, sputtering, CVD,LPCVD, screen printing, spin deposition, dispensing or other techniques.In some embodiments of the present invention layer 5210 may have athickness in the range of about 50 nm to about 1 μm. In some embodimentsof the present invention layer 5210 may have a thickness in the range ofabout 0.1 μm to about 0.5 μm. However the thickness of layer 5210 is nota limitation of the present invention and in other embodiments, layer5210 may have any thickness or be formed by any means.

FIG. 55 is a cross-sectional view of the semiconductor structure of FIG.54 at a later stage of manufacture. After formation of layer 5210, layer5210 may be patterned using photolithography and etching processes toform one or more openings 5310 and one or more openings 5320. Opening5310 in layer 5210 may expose a portion of top contact layer 4510 andopening 5320 in layer 5210 may expose a portion of layer 5110 in mesa410. Portions of layer 5210 may be removed to form opening 5310 and 5320using for example etching techniques, for example isotropic oranisotropic etch process such as, for example, wet chemical etching or areactive ion etch (“RIE”).

FIG. 56 is a cross-sectional view of the semiconductor structure of FIG.55 at a later stage of manufacture. After formation of one or moreopenings 5310 (FIG. 55) and one or more openings 5320 (FIG. 55), layer5410 may be formed over layer 5210, opening 5310 and opening 5320 andpatterned. Layer 5410 may serve several purposes. In some embodiments ofthe present invention a portion of layer 5410 may, through all or aportion of opening 5320, form an electrical or ohmic contact with aportion of bottom confining region 220 directly if layer 5110 is notpresent, or may form an electrical or ohmic contact to layer 5110 whichmay be electrically coupled with bottom confining region 220. In someembodiments of the present invention a portion of layer 5410 may form anelectrical contact with a portion of layer 4510 through opening 5310. Insome embodiments of the present invention a first portion of layer 5410may, through a portion of opening 5320, form an electrical or ohmiccontact with a portion of bottom confining region 220 directly if layer5110 is not present, or may form an electrical or ohmic contact to layer5110 which may be electrically coupled with bottom confining region 220and a second portion of layer 5410 may form an electrical contact with aportion of layer 4510 through opening 5310.

In some embodiments of the present invention layer 5410 may completelycover opening 5310 as shown in FIG. 55, however this is not a limitationof the present invention and in other embodiments layer 5410 may onlypartially cover opening 5310 (FIG. 55). In some embodiments of thepresent invention layer 5410 may only partially cover opening 5320 (FIG.54) as shown in FIG. 55, leaving opening 5320A that is not covered withlayer 5410 and permitting light to escape LED unit 110 through opening5320A. However this is not a limitation of the present invention and inother embodiments layer 5410 may completely cover opening 5320 (FIG.55). In some embodiments of the present invention, as shown in FIGS. 56and 45, layer 5410 may cover a portion of opening 5320 (FIG. 55) nearthe periphery of opening 5320 (FIG. 55), for example layer 5410 mayextend about 0.25 μm to about 10 μm from the edge of opening 5320 (FIG.55).

Referring now to FIGS. 45 and 46, in some embodiments of the presentinvention a first portion of layer 5410 may form contact area 120A and asecond portion of layer 5410 may form contact area 120B. As discussedabove, contact areas 120A and 120B may be used to provide electricalcontact to the light engine. In FIG. 45, layer 5410 is shown as onelayer. However this is not a limitation of the present invention and inother embodiments, layer 5410 may comprise a plurality of layers and/ormaterials. In FIG. 45, layer 5410 is shown as forming both a contact tocontact layer 4510 and to either layer 5110 or bottom confining layer220. However this is not a limitation of the present invention and inother embodiments an additional optional contact layer (not shown) maybe formed, prior to formation of layer 5410, over all or a portion ofopening 5320, thus forming an electrical or ohmic contact with a portionof bottom confining region 220 directly if layer 5110 is not present, ormay form an electrical or ohmic contact to layer 5110 which may beelectrically coupled with bottom confining region 220. In thisembodiment, layer 5410 may then make electrical contact with theadditional contact layer (not shown).

In some embodiments of the present invention, one or more heattreatments may be required to achieve acceptable ohmic contact between aportion of layer 5410 and a portion of bottom confining region 220 iflayer 5110 is not present, or between a portion of layer 5410 and aportion of layer 5110 which may be electrically coupled with bottomconfining region 220.

Acceptable ohmic contact may mean a specific contact resistance of lessthan 1E-3 Ω-cm2, or less than 1E-4 Ω-cm2. Such heat treatments may beperformed, for example, in a furnace, on a hot plate, in a rapid thermalanneal system or the like. Annealing temperatures may range from about300° C. to about 800° C., however the method and time and temperature ofthe anneal process are not limitations of the present invention and inother embodiments, other annealing methods, temperatures or temperatureprofiles, or times may be used. It is important to note that the contactbetween contact layer 4510 and top confining region 240 will alsoreceive the anneal from an anneal of the contact to bottom confiningregion 220. In some embodiments of the present invention, one annealstep may be carried out after formation of both contacts. Annealing maybe done in an inert ambient, for example nitrogen, a reducing ambient,for example forming gas, or any other ambient; the annealing ambient isnot a limitation of the present invention.

In some embodiments of the present invention, it may be desirable tominimize the annealing temperature and/or time or to eliminate theannealing altogether, for example when top contact layer 4510 also actas a mirror. In this example, reduced annealing temperatures and/orelimination of the annealing step or steps altogether may provide ahigher reflectivity to a wavelength of light emitted by thelight-emitting device.

Layer 5410 may comprise one or more layers and may comprise metals,silicides or other conductive materials, for example metals such asgold, silver, aluminum, Au/Ge, Au/Ge/Ni and the like. The specificmaterial(s) used for layer 5410 will depend on the specificsemiconductors in layer structure 250 (FIG. 20). In some embodiments thethickness of layer 5410 may be in the range of about 200 Å to about 5μM, but this is not a limitation of the present invention and in otherembodiments layer 5410 may be any thickness. In some embodiments of thepresent invention layer 5410 may be formed using techniques such asevaporation, sputtering, chemical vapor deposition (CVD), low pressurechemical vapor deposition (LPCVD), oxidation, spin deposition or thelike.

In the example shown in FIG. 46, openings 5310 are shown as having arectangular shape, however this is not a limitation of the presentinvention and in other embodiments 5310 may be square, hexagonal,circular or any arbitrary shape.

In the example shown in FIG. 46, openings 5320 are shown as having arectangular shape, however this is not a limitation of the presentinvention and in other embodiments 5320 may be square, hexagonal,circular or any arbitrary shape.

In the example shown in FIGS. 46 and 55 bottom opening 5310 and opening5320 are shown in the same location in each LED unit 110. However, thisis not a limitation of the present invention and in other embodimentsopening 5310 and opening 5320 may each have different positions on allor some of LED units 110.

In some embodiments of the present invention LED unit 110 (FIGS. 45 and46) may comprise one bottom electrical contact and one top electricalcontact. However, this is not a limitation of the present invention andin other embodiments LED unit 110 may comprise a plurality of bottomelectrical contacts and/or a plurality of top electrical contacts.

In some embodiments of the present invention all or some layers may bechosen on the basis of their properties to improve overall device yieldand/or performance. In some embodiments of the present invention layersthat are provided in an example as a single material may comprise aplurality of materials chosen on the basis of their properties toimprove overall device yield and/or performance. For example, in someembodiments of the present invention attachment layer 1520 and orattachment layer 4520 may comprise a plurality of layers of differentmaterials to reduce the overall strain and/or to increase the mechanicalstrength of semiconductor structure 500.

FIG. 45 is a cross-sectional view of the semiconductor structure of FIG.56 at a later stage of manufacture. After formation of interconnectlayer 5410, optional light conversion material 1810 may be formed overLED units 110 and all or portions of interconnect layer 5410. Optionallight conversion material 1810 may comprise organic or inorganicphosphors or other materials capable of absorption of a portion of orall of the light emitted from active region 230 and re-emitting it at adifferent wavelength. In some embodiments of the present invention lightconversion material 1810 may comprise a down conversion material and inother embodiments light conversion material 1810 may comprise an upconversion material.

In some embodiments of the present invention light conversion materialmay be formed by evaporation, screen printing, ink jet printing, otherprinting methods, CVD, spin deposition or the like. In some embodimentsof the present invention, optional light conversion material 1810 may besuspended or embedded in a second material (not shown), and in someembodiments the second material may comprise a material with an index ofrefraction between that of the material in layer structure 250 (FIG. 20)and air. In one example of this embodiment such second material maycomprise an epoxy, gel or resin with an index of refraction in the rangeof about 1.2 to about 1.7. Such a second material may act to reducetotal internal reflection and increase the light extraction efficiencyof the light engine.

In FIG. 45, light conversion material 1810 is shown as being formed overthe LED units 110. However, this is not a limitation of the presentinvention and in other embodiments light conversion material 1810 may beformed over portions of LED units 110, such that a portion of the lightemitted by active region 230 may exit LED unit 110 directly and aportion of the light emitted by active region 230 may be absorbed in andthen re-emitted by light conversion material 1810. In some embodimentsof the present invention a portion of the light emitted by active region230 may be transmitted through light conversion material 1810 and aportion of light emitted by active region 230 may be absorbed in andthen re-emitted by light conversion material 1810.

In some embodiments of the present invention light conversion material1810 may comprise a plurality of layers or a mixture of different typesof light conversion materials. In some embodiments of the presentinvention, a first light conversion material may be formed over a firstportion of LED units 110 and a second light conversion material may beformed over a second portion of LED units 110. In one example, a firstportion of LED units 110 may be covered with a first light conversionmaterial 1810 that when mixed with the light emitted from the firstportion of LED units 110 produces a warm white color and a secondportion of LED units 110 may be covered with a second light conversionmaterial 1810 that when mixed with the light emitted from the secondportion of LED units 110 produces a cool white color. In one example ofthis embodiment, the LED units associated with the first and secondlight conversion materials may be separately addressable, and thus alight having either warm or cool properties may be created by separatelyturning on LED units 110 associated with either the warm or cool lightconversion materials respectively. In this example both the first andsecond portions of LED units 110 may be turned on creating a neutralwhite color, in between that of cool white and warm white. By varyingthe intensity of light from said first and/or second portions of LEDunits 110, various color temperatures may be achieved. In this exampletwo sub-arrays of LED units 110 and two types of light conversionmaterials 1810 are discussed, however this is not a limitation of thepresent invention and other embodiments may comprise three or moresub-arrays of LED units 110 and three or more different light conversionmaterials 1810. In this example two types of white light, cool and warmare discussed, however this is not a limitation of the present inventionand in other embodiments multiple colors may be produced using thisapproach.

At this point in the manufacture of the semiconductor structure shown inFIG. 45, a plurality of complete light engines is formed on carrier1510. FIGS. 45-56 have shown one light engine; a schematic of the entirewafer at this stage of manufacture is shown in FIG. 38. FIG. 38 shows atop view of the entire wafer at this stage of manufacture, comprisingcarrier 1510 and a plurality light engines 3610 formed on carrier 1510spaced apart from each other by streets 3620. Streets 3620 may have awidth in the range of about 5 μm to about 500 μm. However this is not alimitation of the present invention and in other embodiments, streets3620 may have any width.

After removal of portion of light conversion material 1810 if necessaryand exposing portions of interconnect layer 5410, individual lightengines 3610 may be separated from the semiconductor structure of FIG.38. In other words, the semiconductor structure of FIG. 38 comprises awafer of light engines and the light engines are separated or singulatedfrom the wafer to form separate light engines as shown in FIG. 45.Singulation may be performed using methods such as laser cutting, laserscribing, mechanical scribe and break or dicing. However, this is not alimitation of the present invention and in other embodiments othermethods of separation or singulation may be used.

FIG. 38 shows all light engines 3610 formed on carrier 1510 as havingthe same size. However this is not a limitation of the present inventionand in other embodiments, more than one size light engine may be formedon carrier 1510. In some embodiments of the present invention, differentlight engines formed on carrier 1510 may have different characteristics.For example they may have a different size, a different number of LEDunits, a different color or spectral distribution and thecharacteristics and variation of the characteristics of the lightengines on carrier 1510 are not a limitation of the present invention.

FIG. 57 shows a cross-sectional view of another embodiment of thesemiconductor structure of FIG. 45. In the structure shown in FIG. 57,layer 1520 may be patterned to provide electrical isolation between LEDunits 110 and to form a portion of contact region 120A and a portion ofcontact region 120B and layer 4520 and layer 4510 may be patterned toform a portion of contact region 120A and a portion of contact region120B. In the structure shown in FIG. 57, electrical contact to topconfining region 240 may be made through layer 4510 directly fromcontact region 120A, in contrast to FIG. 45 where contact to topconfining region 240 may be made through layer 5410 and layer 4510. Insome embodiments of this aspect of the present invention, layer 4520and/or layer 1520 may act as a parallel shunt to layer 4510 and maydecrease the lateral resistance from contact region 120A to topconfining region 120A. In some embodiments of this aspect of the presentinvention layer 1520 and/or layer 4520 and/or layer 4510 may bepatterned such that they do not extend into or do not extendsubstantially into contact region 120B and in contact region 120B layer5210 may be formed over carrier 1510 without one or more of theintermediate layers (layers 4610, 1520, 4520 and 4510) in between layer5210 and carrier 1510 in contact region 120B.

FIG. 58 is a cross-sectional view of structure 600 in accordance withanother embodiment of the present invention. The semiconductor structurein FIG. 58 may be referred to as a monolithically formed light system orlight engine. FIG. 59 is a view of the structure of FIG. 58 from thelight emitting side of structure 600, that is side of carrier 1510 overwhich LED units 110 may be formed and FIG. 58 is a cross-sectional viewtaken along section line 58-58 of FIG. 59. In FIG. 59 optional lightconversion material 1810 is not shown, and opening 6302 are shown asdotted lines to indicate that they are under layer 5410.

The monolithic light engine shown schematically in FIG. 58 comprisescarrier 1510, a plurality of LED units 110, layers 1520, 4610 and 4520used to attach LED units 110 to carrier 1510, optional light conversionmaterial 1810, interconnect layer 5410, contact regions 120A and 120Band photonic crystal regions 6202. Carrier 1510 may be referred to as acarrier, a substrate, a mechanical support, a heat sink or a first levelheat sink. Layers 1520 and 4520 may be used to help attach LED units 110to carrier 1510. LED unit 110 may comprise a bottom confining region220, an active region 230, a top confining region 240, a portion oflayer 541, a portion of top contact layer 4510 and a portion of photoniccrystal region 6202.

A photonic crystal may be used to change the direction of lightimpinging on it. Referring now to FIG. 60, 6902 may represent lightincident upon the photonic crystal, 6906 may represent a relativelylarge portion of the incident light that has been caused to be emittedin a direction perpendicular to the surface of the material in which thephotonic crystal is formed and 6904 may represent a relatively smallportion of the incident light that is transmitted through the photoniccrystal. In some prior-art LEDs a photonic crystal may be used as amethod to increase light extraction and thus increase the luminousefficacy. However one problem with the prior-art use of photoniccrystals is that they may cause the material from which they are formedto become non-conductive. Thus a photonic crystal that penetratesthrough the active region may cause a prior-art LED to be opencircuited, at least in the region of the photonic crystal, thus reducingor eliminating the light generating area of the prior-art LED. Inprior-art LEDs this effect may be eliminated by forming the photoniccrystal only in a portion of the epitaxial layer structure above theactive region, thus eliminating the possibility of open-circuiting theLED. The problem with this approach is that the photonic crystal becomesrelatively much less effective. For example, consider layer structure250 (FIG. 20). If the photonic crystal structure penetrates through theentire layer structure, then optical modes in bottom confining region220, active region 230 and top confining region 240 (FIG. 20) may allimpinge on the photonic crystal and may be directed out of the plane oflayer structure 250 (FIG. 20). However if the photonic crystal structurepenetrates only partially into top confining region 240 (FIG. 20), thenonly optical modes within top confining region 240 may impinge on thephotonic crystal structure, resulting in only a portion of light withinthe entire layer structure 250 (FIG. 20) being directed out of the planeof layer structure 250 (FIG. 20). However, in some embodiments of thepresent invention, as will be discussed later, it is advantageous forphotonic crystal region 6202 to be non-conductive and thus in someembodiments of the present invention photonic crystal region 6202 maypenetrate all of or substantially all of layer structure 250 (FIG. 20),resulting in a high efficiency of directing light out perpendicular tothe surface of the light engine. In other words, photonic crystal region6202 may penetrate all or substantially all of layer structure 250 (FIG.20) and cause light directed parallel to the surface of layer structure250 (FIG. 20) to be directed out of each LED unit 110 in a directionperpendicular to the surface of the light engine, thus increasing thelight extraction efficiency and the luminous efficacy.

In some embodiments of this aspect of the invention, formation ofphotonic crystal region 6202 may cause the portions of layer structure250 (FIG. 20) in which photonic crystal region 6202 may be formed to benon-conductive, or insulating. In some embodiments of this aspect of theinvention, formation of a plurality of closely spaced small voids orholes through or substantially through layer structure 250 (FIG. 20) mayresult in surface depletion regions on the surfaces of the photoniccrystal region 6202, wherein said surface depletion regions may fullydeplete the remaining material comprising photonic crystal region 6202,thus rendering photonic crystal region 6202 non-conductive. Anon-conductive photonic crystal region 6202 leads to a reduction in thenumber of steps and layers in the structure and ultimately a reductionin the cost of the light engine. For example, in some embodiments ofthis aspect of the invention, interconnect 5410 may be formed directlyon photonic crystal region 6202 because it is non-conductive,eliminating an isolation layer that may be required in other embodimentsof the present invention. In another example non-conductive photoniccrystal region 6202 may isolate a portion of interconnect 5410 acting ascontact area 120B from the underlying top contact 4510.

Light is generated in active region 230 and exits LED unit 110 throughopening 5320A. Note that in this configuration the light emitting region(opening 5320A) may be larger than in other embodiments of the presentinvention because in this embodiment the regions adjacent to the lightemitting area may be smaller than in some other embodiments of thepresent invention.

In some embodiments of the present invention light extraction features5010 may be formed in or on a portion of LED unit 110 to improve thelight extraction efficiency. In some embodiments of the presentinvention, light extraction features may comprise one or moreanti-reflection coatings and/or surface roughening, texturing,patterning, imprinting or the like. In some examples such lightextraction features may be formed in a regular periodic array, howeverthis is not a limitation of the present invention and in otherembodiments, light extraction features may be formed in a random orsemi-random pattern.

Some of the light generated in active region 230 may exit the activeregion into top confining region 240. Such light may be reflected fromreflecting surfaces that reflect a wavelength of light emitted by theLED that are formed over portions of or all of top confining region 240,for example on the side of top confining region 240 adjacent to carrier1510. In some embodiments of the present invention reflecting surfacesmay also be formed over portions of or all of active region 230 andbottom confining region 220, in particular on all or a portion of thesidewalls of active region 230 and bottom confining region 220. In someembodiments of the present invention, such reflecting surfaces may havea reflectivity greater than 80% to a wavelength of light emitted by theLED, or greater than 90% to a wavelength of light emitted by the LED, orgreater than 95% to a wavelength of light generated in active region230.

Optional light conversion material 1810 may comprise organic orinorganic phosphors or other materials capable of absorption of aportion of the light emitted from active region 230 and re-emitting itat a different wavelength. In some embodiments of the present inventionlight conversion material 1810 may comprise a down conversion materialand in other embodiments light conversion material 1810 may comprise anup conversion material. In some embodiments of the present invention,optional light conversion material 1810 may be suspended or embedded ina second material (not shown), and in some embodiments the secondmaterial may comprise a material with an index of refraction betweenthat of the material in layer structure 250 (FIG. 20) and air. In oneexample of this embodiment such second material may comprise for examplean epoxy, gel, or resin with an index of refraction in the range ofabout 1.2 to about 1.7. Such a second material may act to reduce totalinternal reflection and increase the light extraction efficiency of thelight engine.

LED unit 110 may be formed such that the heat-generating active region230 may be in close proximity to carrier/heat sink 1510, for example allor a portion of active region 230 may be spaced less than 10 μm, or maybe less than 5 μm, or may be less than 2 μm from the surface of carrier1510 adjacent to attachment layer 1520. In other words, the combinedthickness of layer 4610, 1520, 4520, 4510 and top confining region 240may be less than 10 μm, or may be less than 5 μm, or may be less than 2μm. Note that in this embodiment of the present invention, thecombination of thin layer structure 250 (FIG. 20) and non-conductivephotonic crystal 6202 may lead to a relatively planar surface withrelatively small step heights, thus leading to a relatively more simpleand less costly manufacturing process.

Referring now to FIG. 59, FIG. 59 shows a top view example ofsemiconductor structure 500 comprising four (4) LED units 110. In FIG.59 optional light conversion material 1810 is not shown, and openings6302 are shown as dotted lines to indicate that they are under layer5410. In this example LED units 110 are configured as shown in FIG. 10A,comprising two parallel strings of LEDs, each string of LEDs comprisingtwo LED units 110. In this example electrical connection to the positivepolarity terminal of the light engine may be made through contact region120A, which comprises a portion of layer 5410 that may be coupled to thetop confining region 240 of LED units 110 A and B through top contactlayer 4510. Similarly, electrical connection to the negative polarityterminal of the light engine may be made through contact region 120B,which comprises a portion of layer 5410 that may be coupled to bottomconfining region 220 of LED units C and D. Bottom confining region 220of LED units A and B may be electrically coupled to top confining region240 of LED units C and D respectively through a portion of layer 5410.

In the example shown in FIG. 59, LED units 110 are configured as shownschematically in FIG. 10A. However this is not a limitation of thepresent invention and in other embodiments LED units may be connected inany other configuration; the connection topology is not a limitation ofthe present invention. For example, in some embodiments of the presentinvention, the individual LED units may be coupled in series as shown inFIG. 10C, in parallel as shown in FIG. 10B or a combination of seriesand parallel connections as shown in FIG. 10D. In some embodiments, aportion or all of the individual LED units 110 may be coupled anode tocathode as shown in FIGS. 10A to 10D while in other embodiments contactregions 120A and 120B may each have both one or more anodes and one ormore cathodes of individual LED units 110 coupled to them as shown inFIG. 10E, and in other embodiments, a combination of these types ofcouplings may be utilized.

FIGS. 58 and 59 show an exemplary LED array with 4 LED units 110.However, the number of LED units 110 is not a limitation of the presentinvention and in some embodiments the LED array may comprise a largernumbers of LED units 110. In some embodiments of the present inventionthe number of LED units 110 in the array may be greater than 20, or maybe greater than 50, or may be greater than 100 or may be greater than250 or may be greater than 500.

FIG. 61 is a cross-sectional view of a semiconductor structure at anintermediate stage of manufacture that may be used for the furthermanufacture of the semiconductor structure of FIG. 59, in accordancewith an embodiment of the present invention. FIG. 61 is very similar toFIG. 53 as discussed with respect to semiconductor structure 500,however, the patterning of layers 4610, 1520, 4520 and 4510 may bedifferent. As shown in FIG. 61, as compared to FIG. 53, layers 4610,1520, 4520 and 4510 may not be removed near the edge of the light engineperiphery.

Following the stages of manufacture prior to FIG. 61, layer 5110, lightextraction features 5010 and layer structure 250 may be patterned usingphotolithography and etching processes to form one or more openings 6302and one or more photonic crystal regions 6202 as shown in FIG. 62.Openings 6302 may expose a portion of top contact 4510. An isotropic oranisotropic etch process such as, for example, wet chemical etching or areactive ion etch (“RIE”), may be used to form one or more openings 6302and one or more photonic crystal regions 6202. In some embodiments, oneor more openings 6302 and one or more photonic crystal regions 6202 maybe formed in one etch process or step, however this is not a limitationof the present invention and in other embodiments more than one etchprocess or step may be used to form one or more openings 6302 and one ormore photonic crystal regions 6202.

FIG. 63 shows a cross-sectional view of an exemplary semiconductorstructure patterned for a one step process to form the structure of FIG.62. The structure in FIG. 63 comprises a mask 6101 with patterns 6102and 6103. An opening in pattern 6103 may be relatively larger than anopening in pattern 6102. For example an opening in pattern 6103 may bein the range of about 1 μm to about 20 μm whereas an opening in pattern6102 may be in the range of about 2 nm to about 1000 nm. Mask 6101 maycomprise, for example photoresist or a hard mask, as discussedpreviously, however the mask material and method of patterning is not alimitation of the present invention. In some embodiments of this aspectof the invention, one etch step, in conjunction with the mask structureof FIG. 63, the structure of FIG. 64. The structure in FIG. 64 maycomprise one or more openings 6203 and one or more photonic crystal orphotonic lattice regions 6202.

After formation of openings 6302 and photonic crystal regions 6202,layer 5410 may be formed over photonic crystal region 6202, opening 6302and layer 5110 and patterned. Layer 5410 may serve several purposes. Insome embodiments of the present invention a portion of layer 5410 mayform an electrical or ohmic contact with a portion of bottom confiningregion 220 directly if layer 5110 is not present, or may form anelectrical or ohmic contact to layer 5110 which may be electricallycoupled with bottom confining region 220. In some embodiments of thepresent invention a portion of layer 5410 may form an electrical contactwith a portion of layer 4510 through opening 6302. In some embodimentsof the present invention a first portion of layer 5410 may form anelectrical or ohmic contact with a portion of bottom confining region220 directly if layer 5110 is not present, or may form an electrical orohmic contact to layer 5110 which may be electrically coupled withbottom confining region 220 and a second portion of layer 5410 may forman electrical contact with a portion of layer 4510 through opening 6302.

In some embodiments of the present invention layer 5410 may completelycover opening 6302 as shown in FIG. 65, however this is not a limitationof the present invention and in other embodiments layer 5410 may onlypartially cover opening 6302 (FIG. 65). In some embodiments of thepresent invention layer 5410 may only partially cover the exposedportions of layer 5110, or if not present, bottom confining region 220,as shown in FIG. 65, leaving opening 5320A that is not covered withlayer 5410 and permitting light to escape LED unit 110 through opening5320A. However this is not a limitation of the present invention and inother embodiments layer 5410 may completely cover the exposed portionsof layer 5110, or if not present, bottom confining region 220. In someembodiments of the present invention, as shown in FIGS. 58, 59 and 65,layer 5410 may cover a portion of the exposed portions of layer 5110, orif not present, bottom confining region 220 near the periphery of thelight emitting area, for example layer 5410 may extend about 0.25 μm toabout 10 μm into the light emitting area from the boundary of the lightemitting area and photonic crystal region 6202.

Referring now to FIGS. 58 and 59, in some embodiments of the presentinvention a first portion of layer 5410 may form contact area 120A and asecond portion of layer 5410 may form contact area 120B. As discussedabove, contact areas 120A and 120B may be used to provide electricalcontact to the light engine. In FIG. 58, layer 5410 is shown as onelayer. However this is not a limitation of the present invention and inother embodiments, layer 5410 may comprise a plurality of layers and/ormaterials. In FIG. 58, layer 5410 is shown as forming both a contact tocontact layer and to either layer 5110 or bottom confining layer 220.However this is not a limitation of the present invention and in otherembodiments an additional optional contact layer (not shown) may beformed, prior to formation of layer 5410, over all or a portion of layer5110 or bottom confining layer 220, thus forming an electrical or ohmiccontact with a portion of bottom confining region 220 directly if layer5110 is not present, or may form an electrical or ohmic contact to layer5110 which may be electrically coupled with bottom confining region 220.In this embodiment, layer 5410 may then make electrical contact with theadditional contact layer (not shown).

In some embodiments of the present invention, one or more heattreatments may be required to achieve acceptable ohmic contact between aportion of layer 5410 and a portion of bottom confining region 220 iflayer 5110 is not present, or between a portion of layer 5410 and aportion of layer 5110 which may be electrically coupled with bottomconfining region 220.

Acceptable ohmic contact may mean a specific contact resistance of lessthan 1E-3 Ω-cm2, or less than 1E-4 Ω-cm2. Such heat treatments may beperformed, for example, in a furnace, on a hot plate, in a rapid thermalanneal system or the like. Annealing temperatures may range from about300° C. to about 800° C., however the method and time and temperature ofthe anneal process are not limitations of the present invention and inother embodiments, other annealing methods, temperatures or temperatureprofiles, or times may be used. It is important to note that the contactbetween contact layer 4510 and top confining region 240 will alsoreceive the anneal from an anneal of the contact to bottom confiningregion 220. In some embodiments of the present invention, one annealstep may be carried out after formation of both contacts. Annealing maybe done in an inert ambient, for example nitrogen, a reducing ambient,for example forming gas, or any other ambient; the annealing ambient isnot a limitation of the present invention.

In some embodiments of the present invention, it may be desirable tominimize the annealing temperature and/or time or to eliminate theannealing altogether, for example when top contact layer 4510 also actas a mirror. In this example, reduced annealing temperatures and/orelimination of the annealing step or steps altogether may provide ahigher reflectivity to a wavelength of light emitted by thelight-emitting device.

Layer 5410 may comprise one or more layers and may comprise metals,silicides or other conductive materials, for example metals such asgold, silver, aluminum, Au/Ge, Au/Ge/Ni and the like. The specificmaterial(s) used for layer 5410 will depend on the specificsemiconductors in layer structure 250 (FIG. 20). In some embodiments thethickness of layer 5410 may be in the range of about 200 Å to about 5μm, but this is not a limitation of the present invention and in otherembodiments layer 5410 may be any thickness. In some embodiments of thepresent invention layer 5410 may be formed using techniques such asevaporation, sputtering, chemical vapor deposition (CVD), low pressurechemical vapor deposition (LPCVD), oxidation, spin deposition or thelike.

Referring to FIGS. 58 and 59, LED units 110 are shown as having a squareshape, however this is not a limitation of the present invention and inother embodiments LED unit 110 may be rectangular, hexagonal, circularor any arbitrary shape. FIG. 59 shows all LED units 110 having the sameshape, however this is not a limitation of the present invention and inother embodiments a plurality of shapes for LED units 110 may beemployed. FIG. 59 shows each LED unit 110 being spaced apart fromadjacent LED units 110 an equal distance. However, this is not alimitation of the present invention and in other embodiments the spacingbetween LED units 110 may not be equal.

Referring to FIGS. 58 and 59, photonic crystal regions 6202 are shown asbeing formed everywhere on the wafer except for the area used for LEDunits 110. However this is not a limitation of the invention and inother embodiments photonic crystal regions 6202 may be formed on or inonly a portion of the wafer area.

FIG. 59 shows each LED unit 110 being spaced apart from adjacent LEDunits 110 an equal distance. However, this is not a limitation of thepresent invention and in other embodiments the spacing between LED units110 may not be equal.

FIG. 59 shows a particular configuration for the contact to bottomconfining region 240 as being formed around the periphery of opening5320A. However, this is not a limitation of the present invention and inother embodiments any pattern or configuration of metallization orconductive elements may be utilized.

In some embodiments of the present invention, opening 5320A may comprisea square and may have a side length in the range of about 75 μm to about1000 μm. In some embodiments of the present invention opening 5320A maycomprise a square and may have a side length in the range of about 200μm to about 500 μm. In some embodiments of the present invention thespacing between LED units 110 may be uniform and be in the range ofabout 15 μm to about 10,000 μm. In some embodiments of the presentinvention the spacing between LED units 110 may be uniform and be in therange of about 25 μm to about 200 μm.

In the example shown in FIGS. 58 and 59, openings 6302 are shown ashaving a rectangular shape, however this is not a limitation of thepresent invention and in other embodiments openings 6302 may be square,hexagonal, circular or any arbitrary shape.

In the example shown in FIGS. 58 and 59, openings 5320 are shown in thesame location in each LED unit 110. However, this is not a limitation ofthe present invention and in other embodiments opening openings 5320 mayeach have different positions on all or some of LED units 110.

In some embodiments of the present invention LED unit 110 may compriseone bottom electrical contact and one top electrical contact. However,this is not a limitation of the present invention and in otherembodiments LED unit 110 may comprise a plurality of bottom electricalcontacts and/or a plurality of top electrical contacts.

In some embodiments of the present invention all or some layers may bechosen on the basis of their properties to improve overall device yieldand/or performance. In some embodiments of the present invention layersthat are provided in an example as a single material may comprise aplurality of materials chosen on the basis of their properties toimprove overall device yield and/or performance. For example, in someembodiments of the present invention attachment layer 1520 and orattachment layer 4520 may comprise a plurality of layers of differentmaterials to reduce the overall strain and/or to increase the mechanicalstrength of semiconductor structure 600.

FIG. 58 is a cross-sectional view of the semiconductor structure of FIG.65 at a later stage of manufacture. After formation of interconnectlayer 5410, optional light conversion material 1810 may be formed overLED units 110 and all or portions of interconnect layer 5410. Optionallight conversion material 1810 may comprise organic or inorganicphosphors or other materials capable of absorption of a portion of orall of the light emitted from active region 230 and re-emitting it at adifferent wavelength. In some embodiments of the present invention lightconversion material 1810 may comprise a down conversion material and inother embodiments light conversion material 1810 may comprise an upconversion material.

In some embodiments of the present invention light conversion materialmay be formed by evaporation, screen printing, ink jet printing, otherprinting methods, CVD, spin deposition or the like. In some embodimentsof the present invention, optional light conversion material 1810 may besuspended or embedded in a second material (not shown), and in someembodiments the second material may comprise a material with an index ofrefraction between that of the material in layer structure 250 (FIG. 20)and air. In one example of this embodiment such second material maycomprise an epoxy, gel or resin with an index of refraction in the rangeof about 1.2 to about 1.7. Such a second material may act to reducetotal internal reflection and increase the light extraction efficiencyof the light engine.

In FIG. 58, light conversion material 1810 is shown as being formed overthe LED units 110. However, this is not a limitation of the presentinvention and in other embodiments light conversion material 1810 may beformed over portions of LED units 110, such that a portion of the lightemitted by active region 230 may exit LED unit 110 directly and aportion of the light emitted by active region 230 may be absorbed in andthen re-emitted by light conversion material 1810. In some embodimentsof the present invention a portion of the light emitted by active region230 may be transmitted through light conversion material 1810 and aportion of light emitted by active region 230 may be absorbed in andthen re-emitted by light conversion material 1810.

In some embodiments of the present invention light conversion material1810 may comprise a plurality of layers or a mixture of different typesof light conversion materials. In some embodiments of the presentinvention, a first light conversion material may be formed over a firstportion of LED units 110 and a second light conversion material may beformed over a second portion of LED units 110. In one example, a firstportion of LED units 110 may be covered with a first light conversionmaterial 1810 that when mixed with the light emitted from the firstportion of LED units 110 produces a warm white color and a secondportion of LED units 110 may be covered with a second light conversionmaterial 1810 that when mixed with the light emitted from the secondportion of LED units 110 produces a cool white color. In one example ofthis embodiment, the LED units associated with the first and secondlight conversion materials may be separately addressable, and thus alight having either warm or cool properties may be created by separatelyturning on LED units 110 associated with either the warm or cool lightconversion materials respectively. In this example both the first andsecond portions of LED units 110 may be turned on creating a neutralwhite color, in between that of cool white and warm white. By varyingthe intensity of light from said first and/or second portions of LEDunits 110, various color temperatures may be achieved. In this exampletwo sub-arrays of LED units 110 and two types of light conversionmaterials 1810 are discussed, however this is not a limitation of thepresent invention and other embodiments may comprise three or moresub-arrays of LED units 110 and three or more different light conversionmaterials 1810. In this example two types of white light, cool and warmare discussed, however this is not a limitation of the present inventionand in other embodiments multiple colors may be produced using thisapproach.

At this point in the manufacture of the semiconductor structure shown inFIG. 58, a plurality of complete light engines is formed on carrier1510. FIGS. 58-65 have shown one light engine; a schematic of the entirewafer at this stage of manufacture is shown in FIG. 38. FIG. 38 shows atop view of the entire wafer at this stage of manufacture, comprisingcarrier 1510 and a plurality light engines 3610 formed on carrier 1510spaced apart from each other by streets 3620. Streets 3620 may have awidth in the range of about 5 μm to about 500 μm. However this is not alimitation of the present invention and in other embodiments, streets3620 may have any width.

After removal of a portion of light conversion material 1810 (FIG. 58)if necessary and exposing portions of interconnect layer 5410 (FIG. 58)acting as contact areas 120A and 120B (FIG. 58), individual lightengines 3610 may be separated from the semiconductor structure of FIG.38. In other words, the semiconductor structure of FIG. 38 comprises awafer of light engines and the light engines are separated or singulatedfrom the wafer to form separate light engines as shown in FIG. 58.Singulation may be performed using methods such as laser cutting, laserscribing, mechanical scribe and break or dicing. However, this is not alimitation of the present invention and in other embodiments othermethods of separation or singulation may be used.

FIG. 38 shows all light engines 3610 formed on carrier 1510 as havingthe same size. However this is not a limitation of the present inventionand in other embodiments, more than one size light engine may be formedon carrier 1510. In some embodiments of the present invention, differentlight engines formed on carrier 1510 may have different characteristics.For example they may have a different size, a different number of LEDunits, a different color or spectral distribution and thecharacteristics and variation of the characteristics of the lightengines on carrier 1510 are not a limitation of the present invention.

In some embodiments of the present invention in which substrate 210(FIG. 20) may comprise a material that may be transparent and ortranslucent to a wavelength of light emitted by LED unit 110, all ofsubstrate 210 (FIG. 20) may be left in place and the light emitted byLED units 110 may be transmitted from LED units 110 through substrate210 (FIG. 20). In some embodiments of the present invention whereinsubstrate 210 (FIG. 20) may be transparent to a wavelength of lightemitted by LED unit 110, light extraction features may be formed insubstrate 210 (FIG. 20) and/or at the interface of substrate 210 (FIG.20) and layer structure 250 (FIG. 20) or within a region of layerstructure 250 (FIG. 20) adjacent to substrate 210 (FIG. 20) to improvethe light extraction efficiency. In some embodiments of the presentinvention, light extraction features may comprise one or moreanti-reflection coatings and/or surface roughening, texturing,patterning, imprinting or the like. In some examples such lightextraction features may be formed in a regular periodic array, howeverthis is not a limitation of the present invention and in otherembodiments, light extraction features may be formed in a random orsemi-random pattern.

In some embodiments of the present invention wherein substrate 210 (FIG.20) may be transparent to a wavelength of light emitted by LED unit 110,a pattern may be formed in or on substrate 210 (FIG. 20) to aid inhomogenization of the light exiting the light engine or to control orshape the distribution of light exiting the light engine. Such patternsmay be formed, for example by wet or dry (RIE) etching, lapping,polishing, grinding or drilling, however the method of patterningsubstrate 210 (FIG. 20) is not a limitation of the present invention.

In some embodiments of the present invention a light engine may comprisea plurality of interleaved arrays of LED units 110. In other words, thelight engine may comprise, for example a first, second and third arrayof LED units, with each LED units associated with each sub arraypositioned in an intermingled fashion with LED units of other subarrays. FIG. 66 is a schematic of an embodiment of the present inventioncomprising a first sub-array of LED units 110 coupled together and to afirst set of contact regions 120A and 120B and a second sub-array of LEDunits 110′ coupled together and to a second set of contact regions 120A′and 120B′, permitting separately addressable sub-arrays of LED units 110and 110′ within one light engine or LED array. In the example shown inFIG. 66, conductors that are a part of first sub-array of LED units 110may have to cross conductors that are a part of second sub-array of LEDunits 110′ and this crossing is identified in FIG. 66 as 5810. Such acrossing may comprise the two conductors separated by an insulator, butthis is not a limitation of the present invention and crossings 5810 maybe formed using an air bridge, wire bonds, or any other method. In someembodiments of the present invention, sub-arrays may be formed withoutcrossings 5810. The number of sub arrays and the positioning of each LEDunit 110 within each sub array is not a limitation of the presentinvention. In some embodiments of the present invention comprising aplurality of sub arrays of LED units 110, each sub-array of LED units110 may comprise a different light conversion material 1810, resultingin each sub-array of LED units 110 emitting light with a differentcharacteristic or color. In one example, one sub-array of LED units 110may emit “cool” white light while the second sub-array of LED units 110may emit “warm” white light. In another example one sub-array of LEDunits 110 may emit blue light while the second sub-array of LED units110 may emit white light. However, the color emitted by each sub arrayof LED units 110 is not a limitation of the present invention and inother embodiments each sub array of LED units may emit in any color.

In some embodiments of the present invention the light engine maycomprise a plurality of sub-arrays of LED units 110 wherein differentlight conversion materials 1810 may be formed over all or portions ofthe LED units within each sub array. In other words, each sub array ofLED units 110 may be covered or partially covered by a different lightconversion material 1810. In some embodiments of this aspect of theinvention, the different light conversion materials may, with or withouta portion of light emitted directly by active region 230, form aplurality of components of light that collectively make light appearingwhite to the human eye. This is in contrast to the prior art approach ofmixing the phosphors and applying them to one LED die. The approach ofthe present invention may provide improved color quality and LEDluminous efficacy because of several reasons. First, each lightconversion material is separate, thus eliminating losses related toabsorption of a first wavelength of light emitted by first lightconversion material 1810 by a second light conversion material 1810 andthe like. Second by separating the plurality of light conversionmaterials, one relatively better control the intensity of the variouscomponents of light originating from each light conversion materialassociated with the plurality of sub arrays of LED units 110.

In some embodiments of the present invention the light engine maycomprise a plurality of sub-arrays of LED units 110 wherein each subarray of LED units 110 may emit light of the same color andcharacteristic and the total light output of the light engine may bedimmed or reduced by selectively turning off one or more sub-arrays ofLED units 110. One advantage of this approach is that the luminousefficacy of the light engine remains relatively constant under differentlight output levels.

In some embodiments of the present invention, a plurality of sub-arraysof LED units may be coupled to a plurality of driver or electronics andone or more control signals may be received by the plurality of driversor electronics which may then send the appropriate signals to the lightengine to change the color or characteristic of the light emitted by thelight engine. In one example of this embodiment, a plurality ofsub-arrays of LED units may be coupled with a different light conversionmaterial 1810 such that each sub-array of LED units 110 emits light of adifferent color and/or characteristic and by varying the control signalsto the drivers and or the light engine, light of a different color orcharacteristic may be caused to be emitted from the light engine.

In some embodiments of the present invention the light engine maycomprise an array of LED units, one or more conductive elements and oneor more passive and/or active circuit elements, for example conductors,resistors, capacitors, inductors, diodes or transistors. In someembodiments of the present invention the light engine may comprise anarray of LED units, one or more conductive elements and one or morepassive and/or active circuit elements, for example conductors,resistors, capacitors, inductors, diodes or transistors, wherein the LEDunits and one or more conductive elements may be formed monolithicallyon or over a common substrate and one or more passive and/or activecircuit elements may be formed in a hybrid fashion on the commonsubstrate or an adjacent carrier. In some embodiments of the presentinvention the light engine may comprise an array of LED units, one ormore conductive elements and one or more passive and/or active circuitelements, for example conductors, resistors, capacitors, inductors,diodes or transistors, wherein the LED units and one or more conductiveelements and one or more passive and/or active circuit elements may beformed monolithically on a common substrate.

In one example LED units 110 and one or more active and passive circuitelements may be formed in or on or over, for example, substrate 210 ofFIG. 20. In another example LED units 110 may be formed in or on or oversubstrate 210 of FIG. 20 and one or more active and passive elements maybe formed in carrier 1510 of FIG. 32. The method of formation and/ormounting of the passive and/or active circuit element is not alimitation of the present invention. Such active and/or passive circuitelements may be configured to provide additional functionality to thelight engine, for example to control dimming, power management, color,intensity and the like, however the use of the additional circuitelements is not a limitation of the present invention. An advantage ofthis arrangement is that only one set of power lines may be required tobe coupled to the light engine, thus decreasing the number ofconnections to the light engine.

In some embodiments of the present invention all layer structures 250(FIG. 20) in the light engine (for example semiconductor structure 100)may emit light with the same peak wavelength or engineered spectrallight distribution and/or characteristic. However, this is not alimitation of the present invention and in other embodiments, a firstportion of LED units 110 comprising a first portion of layer structures250 may emit light with a first wavelength or with a first engineeredspectral light distribution and/or characteristic and a second portionof LED units 110 comprising a second portion of layer structures 250 mayemit light with a second wavelength or with a second engineered spectrallight distribution and/or characteristic.

FIG. 67 shows an example of a semiconductor structure in which layerstructure 5950 may comprise two light emitting layers. In this examplebottom confining region 220 may be formed over substrate 210, a firstlight emitting layer 5910 may be formed over bottom confining region220, a barrier layer 5920 may be formed over first light emitting layer5910, a second light emitting layer 5930 may be formed over barrierlayer 5920 and top confining region 240 may be formed over second lightemitting layer 5930. In one example the bandgap of first light emittinglayer 5910 may be different than that of second light emitting layer5930 and the bandgap of both first light emitting layer 5910 and secondlight emitting layer 5930 may be less than that of bottom confiningregion 220, barrier layer 4120 and top confining region 240. In theexample shown in FIG. 67 layer structure 5950 comprises two lightemitting layers. However this is not a limitation of the presentinvention and in other embodiments layer structure 5950 may comprise anynumber of light emitting layers.

In some embodiments of a semiconductor structure starting with the layerstructure shown in FIG. 67, all LED units 110 may be associated with thesame light conversion material 1810. However, this is not a limitationof the present invention and in other embodiments, a first portion ofLED units 110 may be associated with a first conversion material 1810and a second portion of LED units 110 may be associated with a secondconversion material 1810. In other embodiments of the present inventiona plurality of LED units may be associated with a plurality of differentlight conversion materials 1810, or may not be associated with any lightconversion material 1810.

In some embodiments of a semiconductor structure starting with the layerstructure shown in FIG. 67, all LED units may be powered or addressedtogether. However, this is not a limitation of the present invention andin other embodiments, a first sub-array of LED units 110 may beaddressed in a separate fashion from a second sub-array of LED units110. In other embodiments a plurality of sub-arrays of LED units may beseparately addressable.

In the examples discussed up to now with respect to FIG. 67, all LEDunits emitted the same light comprising the light emitted from all lightemitting layers in layer structure 5950. However, this is not alimitation of the present invention and in other embodiments differentLED units may emit light of different characteristics.

FIG. 68 is a cross-sectional view of the semiconductor structure of FIG.67 at a later stage of manufacture. After formation of layer structure5950, a portion of top confining region 240 and second light emittinglayer 5930 may be removed over barrier layer 5920 using for examplephotolithography and etching processes. After removal of a portion oftop confining region 240 and second light emitting layer 5930, mesas410A and 410B may be formed using for example photolithography andetching processes. Mesas 410A and 410B form LED units 110 as identifiedin FIG. 17 or 45 with the exception in this example that mesa 410Acomprises bottom confining region 220, first light emitting layer 5910and barrier layer 5920 and mesa 410B comprises bottom confining region220, first light emitting layer 5910, barrier layer 5920, second lightemitting layer 5930 and top confining region 240. In this example mesa410A may result in a first LED unit 110 that emits light characteristicof first light emission layer 5910 and mesa 410B may result in a secondLED unit 110 that emits light characteristic of first light emissionlayer 5910 and second light emission layer 5930.

In the example shown in FIGS. 67 and 68 layer structure 5950 comprisestwo light emitting layers. However this is not a limitation of thepresent invention and in other embodiments layer structure 5950 maycomprise any number of light emitting layers. However, it should berecognized that numerous methods and materials may be used to makeproduce light emission at multiple wavelengths or with an engineeredspectral light distribution and/or characteristic, and these examples donot represent limitations on the invention.

In some embodiments of a semiconductor structure starting with thestructure shown in FIG. 68, all LED units may be associated with thesame light conversion material 1810. However, this is not a limitationof the present invention and in other embodiments, a first portion ofLED units 110 may be associated with a first conversion material 1810and a second portion of LED units 110 may be associated with a secondconversion material 1810. In other embodiments a plurality of LED unitsmay be associated with a plurality of different light conversionmaterials 1810, or may not be associated with any light conversionmaterial 1810.

In some embodiments of a semiconductor structure starting with thestructure shown in FIG. 68 all LED units may be powered or addressedtogether. However, this is not a limitation of the present invention andin other embodiments, a first sub-array of LED units 110 may beaddressed in a separate fashion from a second sub-array of LED units110. In some embodiments of the present invention a plurality ofsub-arrays of LED units may be separately addressable. In someembodiments of the present invention each LED unit 110 may be separatelyaddressable.

In some embodiments of the present invention comprising multiple subarrays, a first sub array may be operated in a pulsed mode with a firstduty cycle and a second sub array may be operated in a pulsed mode witha second duty cycle. In some embodiments of this aspect of the presentinvention, the first and second duty cycle may be varied duringoperation. In some embodiments of this aspect of the present invention,a first sub array may be operated during a first time and a second subarray may be operated during a second later time. In some embodiments ofthis aspect of the present invention, a first sub array and a second subarray may be used to provide redundancy to the light emitting device,for example a first sub array may be operated for a first period oftime, then a second sub array may be operated for a second period oftime and this operational timing may be repeated as desired, for exampleto provide redundancy or to reduce the operating time of each sub array,for example in use in critical applications in which failure of thelight emitting device would cause problems.

In some embodiments of the present invention, LED units may be operatedin pulse mode, with the duty cycle of operation faster than a time ableto be perceived by the human eye, for example less than about 1/120 of asecond.

In this mode of operation the light emitting device may appear to becontinuously on to the human eye while saving energy and operating costby not having the light emitting device operating continuously.

In other embodiments of the present invention a plurality of mesas 410may be formed wherein a first portion of the plurality of mesas 410 emitat a first wavelength or with a first engineered spectral lightdistribution and/or characteristic and a second portion of the pluralityof mesas 410 emit at a second wavelength or with a second engineeredspectral light distribution and/or characteristic.

For example in some embodiments of the present invention, mesas may beformed using a plurality of formation steps. In one example a firstportion of the plurality of mesas 410 may be formed over a first portionof substrate 210 and subsequently a second portion of the plurality ofmesas 410 may be formed over a second portion of substrate 210. In someembodiments, this process may be accomplished using selective depositionor selective epitaxy. In other embodiments, this may be accomplished byforming a first layer structure 250 over substrate 210, patterning andetching portions of first layer structure 250 to remove portions offirst layer structure 250 over substrate 210, forming a second layerstructure 250′ over portions of substrate 210 and first layer structure250, patterning and etching portions of second layer structure 250′ toremove portions of second layer structure 250′ over first layerstructure 250, leaving portions of second layer structure 250′ oversubstrate 210 and forming mesas 410 from portions of first layerstructure 250 and mesas 410′ from portions of second layer structure250′, wherein mesas 410 formed from portions of first layer structure250 may emit a first wavelength or with a first engineered spectrallight distribution and/or characteristic and mesas 410′ formed fromportions of second layer structure 250′ may emit at a second wavelengthor with a second engineered spectral light distribution and/orcharacteristic.

In some embodiments of the present invention, light conversion material1810 and/or all or a portion of LED units 110 and/or all or a portion ofthe light engine may be encapsulated. For example encapsulation may beperformed to protect the light engine and its component parts duringsubsequent manufacturing steps or to simplify subsequent manufacturingsteps. In some embodiments of this aspect of the present invention, saidencapsulation may be performed on the wafer level, for example afterformation of light conversion material 1810. Encapsulation may beperformed using conformal or non-conformal processes, using for exampleevaporation, spin deposition, sputtering, sol gel processing, screenprinting, ink jet printing, dispensing or the like. In some embodimentsof this aspect of the invention, encapsulation may be performed byforming a thin shell over the area or volume to be encapsulated andfilling the space between the shell and the light engine with theencapsulating material. Encapsulation materials may include for example,silicon dioxide, silicon nitride, aluminum nitride, glass, siliconcarbide, epoxy, gels, resins, hydrophobic coatings or the like. Themethod of encapsulation and the encapsulation materials are not alimitation of the present invention.

In some embodiments of the present invention carrier 1510 may beflexible or semi-flexible such that the entire semiconductor structuremay be able to be flexed, bent, curved, rolled or otherwise formed to avariety of shapes such as a cylinder, arch or any other arbitrary shape.In some embodiments of the present invention in which carrier 1510 maybe flexible or semi-flexible, portions of the semiconductor structuremay be removed to permit folding or otherwise formation of a variety ofthree dimensional shapes, for example a sphere, a hemisphere, a cube, orany other shape, with the light emitting surfaces on the inside and/oroutside of the shapes.

In some embodiments of the present invention light conversion material1810 may comprise a material that absorbs all of or substantially all ofthe light emitted by active region 230 and emits light perceived to bewhite by the human eye. In some embodiments of this aspect of thepresent invention, the light engine may be less susceptible torelatively small variations in emission wavelength of active region 230,and thus provide a relatively higher yield with respect to light enginecolor properties.

In some embodiments of the present invention light conversion material1810 may comprise a plurality of layers of light conversion materialswherein said plurality of light conversion materials emits light of adifferent wavelength. In some embodiments of this aspect of theinvention light conversion material may comprise a first lightconversion material 1810 a formed over a second light conversionmaterial 1810 b and a third light conversion material 1810 c formed overlight conversion material 1810 b and light conversion materials 1810 a,1810 b and 1810 c may emit at wavelengths λA, λB and λc such thatλA>λB>λc. In some embodiments of this aspect of the invention, lightfrom active region 230 may be incident upon light conversion material1810 a, a portion of said light may be absorbed in light conversionmaterial 1810 a and re-emitted at wavelength λA, a portion of said lightmay be absorbed in light conversion material 1810 b and re-emitted atwavelength λB and a portion of said light may be absorbed in lightconversion material 1810 c and re-emitted at wavelength λC, such thatthe collective light emitted by the light emitting device is made up ofλA, λB and λc and optionally a portion of light emitted by active region230. In some embodiments of this aspect of the invention, lightconversion material 1810 c may be relatively transparent to light ofwavelengths λA and λB, and light conversion material 1810 b may berelatively transparent to light of wavelengths λA.

In some embodiments of the present invention a planarization layer maybe utilized to reduce the step heights and simplify processing. FIG. 69shows a cross sectional view of a semiconductor structure similar tothat of FIG. 57. The structure of FIG. 69 comprises planarization layer6110 and optional via plugs 6120. Planarization layer 6110 acts to makethe surface of the structure of FIG. 69 more planar and may comprise apolymer such as polyimide or BCB or a dielectric such as silicon oxideor silicon nitride. However the material of planarization layer 6110 isnot a limitation of the present invention and in other embodiments othermaterials may be used. Planarization layer 6110 may be formed usingtechniques such as, for example, spin deposition, CVD, LPCVD,dispensing, however the method of formation of planarization layer 6110is not a limitation of the present invention and in other embodimentsother formation methods may be used. Optional via plug 6120 may beutilized to provide electrical coupling between top contact 4510 andinterconnect layer 5410. Optional via plug 6120 may comprise aconductive material for example a metal or silicide such as Au, Ni, Cu,W, WSi, NSi or the like; the composition of via plug 6120 is not alimitation of the present invention. In some embodiments of the presentinvention where optional via plug 6120 is not utilized, interconnect5410 may make contact directly with top contact 4510. FIG. 61 shows viaplug 6120 as one material, however this is not a limitation of thepresent invention and in other embodiments via plug 6120 may comprise aplurality of materials.

Another aspect of the present invention is structures and methods toreduce testing and binning requirements. Testing and binning is requiredfor prior art LEDs and has been discussed previously. Prior art LEDs aretypically tested on wafer for color, intensity and forward voltage. Thedie are then sorted into bins and sold based on these characteristics.From a lamp manufacturers' perspective, it is desirable to have thehighest available intensity (corresponding to the highest availableluminous efficacy) and color and forward voltage characteristics in asnarrow a range as possible. However, because of the variability of theprior art process, and the fact that the LEDs that are actuallypurchased may come from different wafers and different runs widelyseparated in time, such a tight specification results in a relativelylow yield of LEDs that meet all of these criteria. The relatively lowyield associated with such tight specification of packaged LEDs wouldlead to unacceptably high prices for the packaged LEDs and thus LED lampmanufacturers have to accept LEDs with a wider range of characteristicsthan desired. This leads to either the need for other systems (and cost)to homogenize the characteristics of these LEDs (for example sensors tomeasure the brightness and adjust the current to achieve a specifiedlumen output value or additional testing and binning on the part of thelamp manufacturer) or undesirable variability in the performance of LEDlamps using said LEDs. Such undesired variability has an adverse impacton purchase decisions, while additional systems adds cost, the result ofboth of these is that sales of LED lamps are reduced.

LED lamps comprising the light engine of the present invention may haveless variability in their output characteristics, for example color andintensity than prior art LED lamps because of the more uniformcharacteristics of the light engine and the ability to tune thesecharacteristics on the wafer level, where costs are much less than atthe die, LED package or lamp level. A key feature of LED lampscomprising the light engine of the present invention is that only onelight engine is required per lamp, thus there is no need to test andmatch or control a plurality of packaged LEDs with differentcharacteristics within each lamp.

Improved uniformity of characteristics and reduced testing for lightengines and lamps comprising light engines of the present invention area result of several features and processes associated with the designand manufacture of the light engine and a LED lamp comprising the lightengine of the present invention.

First, the light engine of the present invention is fabricated on waferusing standard integrated circuit (IC) processing techniques and tools.Because the area of the light engine is relatively small compared to thewafer area (the light engine may be about 5 mm by about 5 mm while thewafer may be about 100 mm in diameter or larger), the uniformity of theepitaxial structure (layer structure 250 in FIG. 20) may be quiteuniform over the area of one light engine. Furthermore, because all ofthe LED units within the light engine are fabricated simultaneouslyusing the same processes, the processing-induced variation for the LEDunits comprising the light engine may be relatively smaller than theprocessing-induced variation achievable in LEDs from different wafersand runs manufactured at different times. Thus on an individual lampbasis, the single light engine, comprising a layer structure from a verysmall region of a wafer and LED units all fabricated at the same timeusing the same processing, may provide a more uniform set ofcharacteristics than a plurality of packaged LEDs manufactured atdifferent times and potentially taken from different bins. For example,because the LED units of the light engine of the present invention areall manufactured from an epitaxial structure in a very small region ofthe wafer, the variations in material composition or layer thicknessthat may cause a wavelength variation may be smaller than thatachievable from a plurality of purchased packaged LEDs. In anotherexample, the quality of the layer structure may affect the light outputand luminous efficacy of the LED and, in a similar fashion, thevariations in quality over a small area of a wafer may be relativelysmall. In both cases the variations in these characteristics in aplurality of packaged LEDs may be reduced by purchasing LEDs from narrowbins, however this may greatly increase the cost of said LEDs—incomparison the light engine of the present invention achieves improveduniformity with little to no additional cost.

The next level of variation comes at the lamp level; that is from lampto lamp. For the prior art LED lamp, the same issues are present aswithin each prior art LED lamp, that is the plurality of LEDs havedifferent characteristics and either they must be selected from narrowbins, at increased cost, or they may use additional systems to provide amore homogeneous set of characteristics from lamp to lamp, or arelatively large variation in lamp characteristics may be accepted. Noneof these choices is desirable and various designs and methods of thelight engine of the present invention may act to reduce variations atthe lamp to lamp level, as discussed next.

In some embodiments of the present invention, the light engines may betested on wafer and their spectral and electrical characteristicsrecorded, for example including color, intensity and I-Vcharacteristics. Note that this is testing of the light engine, not theLED units comprising the light engine. In an embodiment of this aspectof the invention (situation 1) of this aspect of the present inventionthe uniformity on wafer and from wafer to wafer is sufficient forcommercial purposes and no additional processing is necessary (this maybe the case for a light engine with or without light conversionmaterial. In another embodiment of this aspect of the invention(situation 2), the uniformity variation across the wafer is known andrelatively the same from wafer to wafer and in this situation action maybe taken on a wafer level without the need to test every wafer—wafertesting may be done on a periodic basis in this situation. In anotherembodiment of this aspect of the invention (situation 3), the uniformityvariation across the wafer is not constant, either within a depositionprocess (i.e. from wafer to wafer within one run) for the epitaxiallayer structure (for example layer structure 250 (FIG. 20) or from runto run. In this situation action may be taken on a wafer level based onthe results of testing of the light engine and not testing of individualLED die as must be done in prior art LEDs and LED lamps.

Several actions may be taken as part of various embodiments of thepresent invention. These will be discussed in the context of a lightengine comprising light conversion material, for the production of whatis generally termed white light. However this is not a limitation of thepresent invention and in other embodiments these actions may beapplicable to light engines of the present invention emitting othercolor lights or, where applicable, light engines of the presentinvention with no light conversion material. The various actions to bedescribed below may be applicable to situation 1 and situation 2; thedifference is in the frequency of testing required to get the requireddata.

In some embodiments of this aspect of the invention, the amount of lightconversion material formed over each light engine on the wafer iscalculated from the map of color distribution (emission wavelength) andintensity distribution across the wafer, and the correct amount of lightconversion material for each light engine is formed over each lightengine on the wafer level. The light from the light engine is compriseof light emitted by the light conversion material and in some cases aportion of the light emitted directly from active region from all or aportion of LED units of the light engine. In some embodiments of thisaspect of the invention, an automated system may be employed to form ordispense the correct amount of light conversion material over each lightengine of the present invention.

In some embodiments of this aspect of the invention, it may not bepossible to adequately correct for the color and intensity variation ona wafer only by the amount of light conversion material to be formedover the light engine, and in this situation a plurality of lightconversion materials may be utilized in conjunction with the wafer mapof color and intensity to form or dispense two or more different lightconversion materials on all or a portion of LED units comprising thelight engine. In some embodiments of this aspect of the invention, afirst light conversion material may be formed over a first portion ofLED units and a second light conversion material may be formed over asecond portion of LED units within each light engine to provide thedesired output color. In some embodiments of this aspect of theinvention, a first and second light conversion material may be mixed andapplied to all or a portion of LED units of the present invention. Insome embodiments of this aspect of the invention both the amount andtype of light conversion material may be varied, however this is not alimitation of the present invention and in other embodiments only theamount or only the type of light conversion material may be varied.

In some embodiments of this aspect of the invention, the lightconversion material may be dispensed using high speed dispensing tools,however this is not a limitation of the present invention and in otherembodiments other methods of forming the light conversion material maybe employed. In one example the light conversion material or materialsmay be printed, for example using ink jet or other technologies, on thewafer and in one example of this approach an ink jet print head coveringthe entire wafer area with individual print heads corresponding to eachlight engine on the wafer may be employed to form or dispense thecorrect and appropriate light conversion material on all light enginessimultaneously. It is important to note that testing and formation ofthe correct and appropriate amount of light conversion material is doneon the wafer level, where automated, high speed process tools may beemployed to minimize costs.

FIG. 70 is a wafer comprising light engines where the color andintensity distribution has been divided into three groups 6210, 6220 and6230. In some embodiments of this aspect of the invention the lightengines in each group may receive a different amount of light conversionmaterial. In some embodiments of this aspect of the invention the lightengines in each group may receive a different type and/or amount oflight conversion material.

In some embodiments of the present invention, light conversion material1810 may be chosen and formed in a way to absorb all or substantiallyall of the light emitted directly by active region 230. In someembodiments of this aspect of the invention, this may reduce thesensitivity of the color of light emitted by the light engine to theemission wavelength or color of the light emitted by the LED unitscomprising the light engine. In some embodiments of this aspect of theinvention, light conversion material may comprise a material that, whenexcited by light of a wavelength emitted by active region 230, re-emitslight that may appear white to the human eye. Such a phosphor may emit(re-emit) at several wavelengths to create the impression of white lightto the human eye, for example in three wavelength ranges inapproximately the red, green and blue regions of the spectrum. Such alight conversion material may be called a tri-color light conversionmaterial or a tri-color phosphor. Said light conversion material may beless sensitive to small variations in the excitation wavelength (thelight emitted from active region 230) and thus may lead to a moreuniform color across the wafer of light engines and from wafer to waferand batch to batch.

Such tri-color light conversion materials typically have a lowerefficiency than materials used for white LEDs wherein a portion of thelight emitted directly by the LED is mixed with the light re-emitted bythe light conversion material. Such a lower efficiency further reducesthe luminous efficacy of prior-art LEDs and LED lamps and thus suchmaterials are not widely used. In the present invention, this may beless of a problem because the LED units of the light engine are operatedat near peak luminous efficacy (low current or current density) and thusit may be desirable in the case of the present invention to trade off asmall amount of reduction in luminous efficacy for an improvement incolor uniformity and a corresponding reduction in the necessity oftesting and binning. In some embodiments of this aspect of the presentinvention, the number of LED units in the light engine may be increasedat relatively little cost to achieve a particular luminous flux of thelight engine or LED lamp when using such light conversion materials(i.e. tri-color). The small increase in manufacturing cost associatedwith an increase in the number of LED units per light engine may be morethan offset by the increased yield and reduced testing and binningrequirements and may also result in an overall reduction in cost.

Another issue related to the use of light conversion materials is thattheir performance, and in particular their efficiency and in some caseslifetime may decrease at elevated temperatures. In the prior-artapproach where LEDs are operated at high current or current densitylevels, a relatively large amount of heat is generated resulting in afurther decrease in light output as well as a color shift forconfigurations where the emitted light comprises a portion of the lightemitted from the active region 230 and a portion of light re-emitted bylight conversion material 1810. The result of this is that the color ofthe prior art LED or prior art LED lamp may shift as a function of drivecurrent (intensity) and lifetime. In prior-art LEDs one way to mitigatethis is to locate the light conversion material some distance away fromthe die (sometimes called remote phosphor) in an attempt to keep thelight conversion material relatively cooler. While this approach mayhave some benefits, it increases the manufacturing complexity as well ascost and in general is undesirable. In some embodiments of the presentinvention the sensitivity of the light conversion material to heat maybe relatively greatly reduced because of the relatively lower amount ofheat generated in comparison to prior art LEDs. The light engine of thepresent invention may generate about 2× to about 3× less heat than priorart LEDs, and thus may cause relatively much smaller thermally-inducedvariations in the efficiency and lifetime of the light conversionmaterials in comparison to prior art LEDs and lamps.

In some embodiments of the present invention only the light intensityvariation may need to be corrected, for example in the case of using atri-color phosphor, as discussed above. Light intensity may correspondto a variation in luminous efficacy, and this is typically about 30%across a 3″ or 4″ diameter wafer. Luminous efficacy variation across awafer is typically in the range of about 30%. In one example the peakluminous efficacy may be about 143 lm/W, the mean value may be about 110lm/W and the minimum value may be about 77 lm/W. FIG. 71 shows such adistribution of luminous efficacy across a wafer. Marker 6380corresponds to about the mean of the distribution and marker 6390 maycorrespond to a minimum acceptable value of luminous efficacy.

In one embodiment of the present invention, light engines having aluminous efficacy between markers 6390 and 6380 may comprise a firstlight conversion material and light engines having a luminous efficacygreater than marker 6380 may comprise a second light conversion materialwherein said first light conversion material comprises a cold whitelight conversion material and said second light conversion materialcomprises a warm white light conversion material. Warm white lightconversion materials typically have a relatively lower efficiency thancold white light conversion materials, for example about a 15% to about20% lower efficiency. Applying the relatively lower efficiency secondlight conversion material to light engines with a relatively higherluminous efficacy and applying the relatively higher efficiency lightconversion material to light engines with a relatively lower luminousefficacy may result in the ability to use all light engines, with alllight engines producing substantially the same amount of light (sameluminous efficacy) but with different color temperatures, thus resultingin increased yields and lower costs. In one example marker 6390 maycorrespond to about 95 lm/W and marker 6380 may correspond to about 110lm/W and using a relative efficiency of about 100% for the cold whitephosphor and about 85% for the warm white phosphor results in a luminousefficacy for the cold white light engine in the range of about 95 lm/Wto about 110 lm/W and a minimum luminous efficacy for the warm whitelight of about 93.5 lm/W. The maximum of the luminous efficacydistribution is about 143 lm/W, which would correspond to about 121 lm/Wwith the cold white phosphor. To maintain the same range of luminousefficacy as the warm white light engines, the upper acceptable limitwould be about 129 lm/W. The result of this approach is that many moreof the light engines may be used in lamps without the need for intensitybinning.

In some embodiments of this aspect of the invention, light intensity orluminous efficacy correction may be performed by a light sensor formedon the light engine or within the LED lamp that measures the lightoutput and provides a correction signal to the driver electronics tochange the power to the light engine to achieve the desired luminousflux. In some embodiments of this aspect of the invention, the driverelectronics, in response to the sensor signal, may increase or decreasethe current to the light engine. In some embodiments of this aspect ofthe invention, the light sensor may be integrated on or in the lightengine and may be formed from all or a portion of the layers used toform the LED units.

In some embodiments of this aspect of the invention, the light enginemay comprise additional LED units which are not initially electricallycoupled to the light engine and/or may comprise a portion of the LEDunits which may be removed from the LED array after fabrication. Inresponse to a map of intensity across the wafer, the additional orremovable LED units may be added or removed to bring the intensity (orluminous flux) within the specified range. FIG. 72A shows a top view ofa light engine of the present invention comprising contact areas 120Aand 120B, a main array of LED units 110, a string of LED units capableof being removed from the main array identified as 6330, a string of LEDunits capable of being added to the main array identified as 6350,removal points 6340 and addition points 6360. Removal of LED string 6330may be accomplished by removal of the conductive elements associatedwith removal points 6340, for example by laser cutting, however this isnot a limitation of the present invention and in other embodiments othermethods of removal of LED string 6330 may be employed. Addition of LEDstring 6350 may be accomplished by adding conductive elements associatedat the addition points 6360 to electrically couple LED string 6350 tocontact areas 120A and 120B, for example by optically enhanced CVD,local metallization or the like, however this is not a limitation of thepresent invention and in other embodiments other methods of adding LEDstring 6350 may be employed.

FIG. 72B shows an exemplary distribution of characteristics across awafer of light engines of the present invention. The lower specificationlimit (LSL) and upper specification limit (USL) are shown on thedistribution indicating the portion of the distribution that is withinthe specifications across the wafer. The portions of the distributionbetween 6310 and LSL and between ULS and 6320 are the portions that maybe brought into the specification range by adding or removing LEDs 6350or 6360 respectively. For example, if the intensity of a particularlight engine is low LEDs 6350 may be added to that particular lightengine and if the intensity of a particular light engine is too high,LEDs 6330 may be removed from that particular light engine. In someembodiments of this aspect of the invention, each light engine may haveboth removable and addable LEDs, however this is not a limitation of thepresent invention and in other embodiments each light engine may haveonly removable LEDs or only addable LEDs. By using addable and removableLEDs, the portion of light engines that are within the specificationlimits may be relatively greatly increased.

In some embodiments of the present invention, light conversion material1810 may be mixed with at least one second material, for example anepoxy or resin or other material that may be cured using visible orultraviolet (UV) light. In some embodiments of this aspect of theinvention, after material 1810 and said second material are formed ordispensed over all or portions of the light engine, said second materialmay be cured by irradiation of light of the appropriate wavelength, thusfixing the phosphor in place on the light engine. In some embodiments ofthis aspect of the invention, this may be done when the light enginesare in wafer form; that is before singulation. In some embodiments ofthis aspect of the invention, the same tool may apply light conversionmaterial 1810 and said second material and effect the curing of saidsecond material. In some embodiments of this aspect of the invention,curing may be effected by energizing the light engine, whereby the LEDunits of the light engine provide light of the appropriate wavelength tocure said second material.

Another aspect of the present invention comprises a lamp or luminairecomprising a light engine of the present invention and in particular alamp comprising a monolithically formed light engine. A key feature ofthis aspect of the present invention is a lamp with relatively higherluminous efficacy and relatively significantly lower cost. As discussedpreviously prior art LED lamps and luminaires are made using a pluralityof individually packaged LEDs that are mounted on a carrier or circuitboard that provides electrical coupling between the individual packagedLEDs and the power supply and provides thermal coupling to remove heatgenerated by the individual packaged LEDs. The cost of the individualpackaged LEDs and their assembly on the carrier or circuit boardrepresent a significant portion of the cost of prior art LED lamps andluminaires. Because individual packaged LEDs have variability in theirintensity (luminous efficacy), color and I-V characteristics, the LEDmanufacturers have to bin the LEDs, that is test and separate them intoa number of categories for use by lamp or luminaire manufacturers. Thisleads to a lower yield of packaged LEDs that meet the lampmanufacturer's specifications and thus higher costs. For example, atypical LED process may have 8 color bins, 3 flux bins and 4 forwardvoltage bins. If the a customer desires to specify a portion of the LEDsfrom each category, for example they will take 30% of the availablecolor bins, 55% of the available flux bins and 70% of the availableforward voltage bins, the best yield for this choice is only about 11%of the full distribution. Such a low yield is not commerciallyacceptable, and thus at this point in time, manufacturers are limited toselecting portions of only one, or perhaps two of the three bins. Forexample if one prioritizes on color and accepts variations in forwardvoltage or flux, or one prioritizes on flux and accepts variations incolor and forward voltage, the expected yield from these selectionsincreases to about 70% to about 80% of the full distribution (JeffreyPerkins, Yole Development, “LED Manufacturing Technologies and Costs,”DOE SSL Workshop, Fairfax, Va. April 2009).

There is accordingly a need for improved LED lamps and luminaires, andspecifically a need for LED lamps with higher luminous efficacy andlower cost.

FIG. 73 shows a cross-sectional view of a lamp comprising a light engineof the present invention. The lamp has a modular design resulting inrelatively easy and short assembly times and with a relatively lowassembly cost. The lamp and each module are designed for automatedassembly to further reduce costs and assembly time. The lamp in FIG. 73comprises light engine 7310, an electronics module 7330, an opticsmodule 7360, a housing 7390 and a base 7398.

Attributes of the LED lamp of the present invention may include a LEDlamp luminous efficacy greater than about 100 lm/W and a total lightoutput from the LED lamp greater than about 1000 lm or greater thanabout 1500 lm. Key features of the LED lamp of the present invention mayinclude (1) the ability to configure the connections between individualLED units comprising the array to match the maximal efficiency of theAC/DC power converter and LED driver to reduce electrical losses, (2)integration of the light engine with the lamp optics to reduce opticallosses, integration of the light engine and electronics in a completethermal management system to reduce overall heat generation and improveheat dissipation and system lifetime and integration of all aspects ofthe lamp design and manufacturing to reduce cost and increase luminousefficacy and lifetime.

In contrast to prior-art LED lamps, only one light engine needs to bemounted in the LED lamp of the present invention, thus greatly reducingassembly complexity and cost, increasing reliability, and alsoeliminating the cost of multiple packaged LEDs—the package cost can be avery significant portion of the entire cost, often more than the LED dieitself.

In contrast to prior-art LED lamps, in the LED lamp of the presentinvention the optics may be optically coupled to the light engine,reducing the number of different index of refraction interfaces, thusdecreasing optical losses and additional heat generation by absorption.

The light engine of the present invention may be provided with powerfrom a power converter and/or LED driver. The input to the LED lamp ofthe present invention may typically be an AC voltage, for example 120VACat about 60 Hz in the United States, and this may be provided throughthe lamp base. This is the widespread AC power available in residencesand businesses. However, LEDs operate typically in a DC mode, and thususually some type of power converter (to convert the 120VAC to arelatively lower DC voltage) and LED driver (to provide a constant drivecurrent to the LEDs) may be incorporated into the LED lamp. This isdesirable, as opposed to having the AC/DC converter and or LED driverexternal to the LED lamp, because an internal configuration permits easyreplacement of conventional bulbs with LED bulbs with no change to theelectrical or mechanical infrastructure. However, this is not alimitation of the present invention and in some embodiments the LED lampmay comprise an electronics module to permit operation of the LED lampon AC power and in some embodiments the LED lamp may operate on DCpower.

In some embodiments off-the-shelf power converters and/or LED driversmay be used. In this situation, these electrical circuits may beanalyzed to determine the output voltage and current from these devicesthat result in the highest electrical efficiency. In some cases for thepower converter, an output voltage closer to the input voltage mayresult in a higher electrical efficiency. The array in the light enginemay then be configured to match the maximal efficiency output voltage ofthe power converter and/or LED driver. This may be done by connectingthe LED units comprising the array in a series and/or parallel array. Insome embodiments of the present invention each LED unit may have anoperating voltage of about 3 V. If the optimal output voltage of theelectronics system is about 45 volts, then the number of LEDs in seriesto best match this may be determined by dividing the driver outputvoltage by the LED voltage (45/3) resulting in about 15 LEDs in seriesto achieve about a 45V load. Each LED unit may provide about 8 lumens,and thus each series string may provide about 8 lm*15 LEDs or about 120lumens. The number of strings in parallel may be determined by dividingthe total desired lumen output by the lumen value per string. Forexample if the desired lumen output is about 1000 lumens, then thenumber of strings required is about 1000/120 or about 8 or about 9. Thisexample has been simplified because no correction factors are used forelectrical and optical losses. For example, if the electrical efficiencyis about 85% and the optical efficiency of the optics and housing isabout 85%, then the required amount of initial lumens from the lightengine is about 1000/0.85/0.85 or about 1384 lumens. This gross amountof light may need to be further increased if there is a need to de-ratethe light output of the light engine because of the need to operate itat relatively higher temperatures. However, it is an aim of thisinvention to operate the light engine at relatively low temperaturescompared to prior-art LED lamps, and thus minimize or eliminate the needfor temperature-related de-rating. It is another aim of this inventionto use an integrated approach to designing the in a modular fashion tominimize efficiency losses in all areas and thus to achieve relativelyhigh luminous efficacy compared to prior are LED lamps.

As discussed previously the light engine generates relatively less heatcompared to prior-art LEDs, in some examples about 2-3× less heat, andthus the requirements of the thermal management system are relativelyrelaxed. In some embodiments of the present invention the junctiontemperature of the LED units in the light engine may be less than 65°C., or less than 60° C., or less than 55° C., or less than 50° C. Thismay be significantly lower than typical junction temperatures for priorart LEDs or LED lamps, which typically are at least about 85° C. Thelight engine may be mounted to the thermal management system, which insome examples may comprise a support structure with a relatively highthermal conductivity. In some examples this may be a metal, for example,Al, Cu, brass or other metals, or materials such as silicon, AlN, SiC orothers. In some examples the support structure may be formed of the samemetal as is used in all or a portion of the lamp housing and/or lampbase and/or electronics module. The electronics may also be mounted tothe support structure in some examples. The support structure may bepart of the lamp housing and/or lamp base, or may be coupled to themthrough a relatively high thermal conductivity pathway. In some examplesthe support structure and/or lamp housing and/or lamp base may act as aheat sink or a thermal conduction pathway to transfer heat away from thelight engine and to the lamp housing, lamp base and possibly the lampsocket.

Another advantage of the relatively low heat generation and relativelylow junction temperature is that the LED lamp of the present inventionmay have a significantly longer lifetime than prior art LED lamps. It iswell known that the light output of LEDs decreases with time (they donot “burn out” as do incandescent lamps) and the rate of decreaseincreases with increasing operating or junction temperature. Thus theLED lamps of the present disclosure may have a relatively longeroperating time (as defined as the time to get to 70% (or any othervalue) of the initial light output. The difference in lifetime of LEDsoperated at 64° C. and 74° C. is about a factor of two longer at thelower temperature.

In other embodiments of the present invention, the LED lamp may comprisea light engine comprising a hybrid array of relatively small LED unitsoperated near peak efficiency, mounted on a carrier or a circuit board.

In other embodiments of the present invention, a portion or all of therequired electronics may be formed in or on the light engine. In someexamples a portion of the electronics may be formed in the material usedto make the LED, and in other examples the electronics may be formed ina carrier that supports the LED material. In other examples, all or aportion of the electronics may be mounted to the light engine in ahybrid fashion. In one example a portion or all of the electronics maybe formed in a silicon carrier to which the LED material is attached. Inanother example one or more power conversion chips, driver chips and orother circuitry, for example resistors, capacitors, inductors,transistors, diodes, etc, may be mounted on the LED material and/or thecarrier.

In another embodiment of the present invention, a custom or partiallycustom designed electronics package may be utilized (as opposed to anof-the-shelf) electronics package, to permit improved optimization andmatching of the electronics to the light engine to provide increasedluminous efficacy, lower cost, enhanced functionality, greaterreliability, simplified manufacturing or for other reasons. Such acustom, or partially custom electronics package may be monolithicallyintegrated with the light engine, mounted on the light engine, ormounted within the lamp housing, for example on the thermal managementsystem.

As discussed above, the optics may be optically coupled to the lightengine to minimize the number of different interfaces between the LEDdie and the exterior of the lamp. Schematically this is shown in FIG.73, in which a single optical system is optically coupled to a singlelight engine. Light enters the optical system and is appropriatelyshaped and exits through a lens or other such surface. This designeliminates the multiple air interfaces that exist within prior-art LEDs.

Light engine 7310 has been described previously, and at this stage,comprises the complete light emitting component of the lamp. In someembodiments of the present invention light engine 7310 may comprise twocontacts for electrical coupling to the LED driver. However this is nota limitation of the present invention and in other embodiments lightengine 7310 may comprise more than two contacts, for example in order toseparately control a plurality of sub-arrays of LED units in lightengine 7310. In another example, more than two contacts may be used toelectrically couple the driver to light engine 7310.

In some embodiments of the present invention electronics module 7330 maycomprise a mounting element 7332 and electronics 7334. In someembodiments of the present invention electronics module 7330 maycomprise components required to operate light engine 7310 from AC power.In some embodiments of the present invention electronics module 7330 mayconvert AC voltage to DC voltage and provide a constant current sourcefor light engine 7310. However, this is not a limitation of the presentinvention and in other embodiments electronics module 7330 may provideany type of power to light engine 7310, for example, a constant DCcurrent, a varying DC current, a pulsed DC current, an AC voltage or anyarbitrary voltage and current signal.

In some embodiments of the present invention, electronics 7334 maycomprise a driver chip and associated circuitry, for example comprisingone or more conductive elements, one or active elements such as atransistor or diode and/or one or more passive elements such as aresistor, capacitor, inductor. FIG. 74 shows an example of a LED drivercircuit using a Maxim 16802B LED driver chip. In this example the lightengine would have contact pads for the drain, gate and source oftransistor Q1 as well as both terminals of the LED array.

Additional key components include inductor L1, transistor Q1 and dioded1. Losses may occur in these elements which contribute to reducing theoverall efficiency of the electronics module. In particular, in systemsemploying a form of switching to carry out the power conversion and ordriver function, the external transistor(s) and diode(s) are switchedoff and on at a high rate (hundreds of kilohertz to hundreds ofmegahertz) and thus any switching losses in these components maycontribute significantly to the overall losses in the system.

A key measure for evaluating the electrical losses that may be incurredin an active device such as a transistor or diode is the on resistance.There are many different designs for diodes and transistors that havebeen developed to reduce the on resistance, but an intrinsic limit isthe volume resistance of the semiconductor material through which theelectrical current must flow. In large measure this is determined by howlarge a voltage the device must be able to support in the off state.Each material has critical breakdown field strength, for examplemeasured in V/cm. For a particular material this is fixed, and thus aminimum volume of material is required to support a voltage across thedevice in the off state. When the device turns on, the electricalcurrent must flow through this volume—the larger the volume (length) ofthis material, the higher the on resistance. Thus the higher thebreakdown field strength, the less volume of material is required, andthe lower the on resistance. Most such devices are currently made usingsilicon which has a breakdown field strength of about 3 E5 V/cm. Othermaterials, for example SiC or GaN, have higher breakdown field strengthsof about 1-3 E6 and 5E6 V/cm respectively. The thickness of materialrequired to support a given off-state voltage is proportional to thesquare root of the breakdown field strength, and thus GaN may have anintrinsic on resistance about 3× lower than that of silicon. Thedifficulty in this approach is that the devices in which a low onresistance is desired must be made of a different and typically muchmore expensive material resulting in higher overall cost.

In some embodiments of the present invention, the layout of the LEDunits and contact areas may be made such that is additional space inwhich one or more diodes or transistors may be formed on or in layerstructure 250 (FIG. 20). In some embodiments of this aspect of theinvention, layer structure 250 (FIG. 20) may comprise a material with arelatively large bandgap, for example larger than about 1.7 eV or largerthan about 2.5 eV. Examples of materials with relatively large bandgapsinclude SiC, GaN, AlGaN, InGaN and the like. This provides severaladvantages. First, the circuit elements may have a lower on resistancethan those in relatively lower bandgap materials such as silicon becauseof the much higher breakdown field strength in the relatively widerbandgap materials. Second, these devices will be integratedmonolithically on the light engine substrate, thus reducing the partscount, cost and number of connections. In some embodiments, circuitelements such as resistors, capacitors and inductors may also bemonolithically incorporated on the light engine substrate. Even if thesedo not take advantage of the higher breakdown field strength ofrelatively wider bandgap materials, they reduce the parts count, costand number of connections. These features may also lead to increasedreliability. In some embodiments of this aspect of the invention thelayer structure for the electronic circuit elements may be formed orgrown over the same substrate as used for the layer structure for thelight emitting device. In some embodiments of this aspect of theinvention the electronic circuit elements may be formed in all or aportion of the layer structure for the light emitting device. In someembodiments of this aspect of the invention the electronic circuitelements may be electrically coupled to one or more LED units comprisingthe light engine, however this is not a limitation of the presentinvention and in other embodiments the electronic circuit elements maybe electrically coupled to other components in electronics module 7330or the electronic circuit elements may be electrically coupled to one ormore LED units comprising the light engine and to other components inelectronics module 7330.

FIG. 75 shows a schematic layout of an LED array comprising contactareas 120A and 120B, LED units 110, a FET transistor 7410 and a diode7420. In some embodiments of the present invention transistor 7410 maycorrespond to transistor Q1 in FIG. 74 and diode 7420 may correspond todiode D1 in FIG. 74. Contact area 7412 may be electrically coupled to asource region 7450 of transistor 7410. One terminal of diode 7420 may beelectrically coupled to contact area 7430 and to a drain region 7452 oftransistor 7410 and the other terminal of diode 7420 may be electricallyto contact area 120B. Contact area 7414 may be electrically coupled togate region 7454 of transistor 7410. The configuration shown in FIG. 75is similar to that shown in the circuit schematic of FIG. 74. Externalcomponents may be electrically coupled to contact area 7414, 7420 andcontact areas 120A and 120B.

In some embodiments of the present invention, light engine 7310 may bemounted on one side of mounting element 7332 and electronics 7334 may bemounted on the opposite side of mounting element 7332. The contacts onlight engine 7310, for example contact areas 120A and 120B (FIG. 17) maybe electrically coupled to electronics 7334 through conductive elements7336 which may pass through mounting element 7332. In some embodimentsof the present invention conductive elements 7336 may be electricallyisolated from light engine 7310 and/or electronics 7334. Electricalcoupling of conductive elements 7336 to contact areas 120A and 120B onlight engine 7310 may comprise bond wires, soldering, pressure contacts,snap contacts or the like, the method of electrical coupling is not alimitation of the present invention.

In some embodiments of the present invention, a portion or all ofmounting element 7332 and optionally a portion or all of additionalstructural components of electronics module 7330 may comprise a thermalmanagement system or part of a thermal management system, for example aheat sink, to aid in removal of heat generated by light engine 7310 andelectronics 7334. In some embodiments of this aspect of the inventionthe thermal management system may comprise all or a portion of base7398, all or a portion of housing 7390, all or a portion of mountingelement 7332 and/or all or a portion of electronics module 7330.

In some embodiments of the present invention base 7398 may comprise astandard base that mates to commercially available sockets, for examplean Edison screw base (E10, E11, E12, E14, E17, E26, E27 or the like), abayonet mount or a pin base. However, this is not a limitation of thepresent invention and in other embodiments base 10020 may be any type ofbase, including a custom base made especially for one or more specialtylamps or luminaires or lighting systems. In some embodiments of thepresent invention, the electrical contacts on base 7398 may beelectrically coupled to electronics 7334 by conductive elements 7337.

Mounting element 7332 may comprise a recess into which light engine 7310may be mounted. However this is not a limitation of the presentinvention and in other embodiments light engine 7310 may be mounted overmounting element 7332 without a recess in mounting element 7332. Lightengine 7310 may be mounted over mounting element 7332 using a variety oftechniques, for example soldering, epoxy, adhesive, press fit or thelike, the method of mounting light engine 7310 to mounting element 7332is not a limitation of the present invention.

FIG. 76 shows an example of optics module 7360. Optics module 7630 maycomprise a single optical element 7610 optically coupled to light engine7310. Optical element 7610 may act to focus and/or shape the lightemitted by light engine 7310 to the desired illumination pattern. Forexample illumination patterns may include a spot pattern in which thelight is relatively tightly focused to a relatively small spot, a floodpattern providing a broad distribution of light or any other pattern,the light pattern is not a limitation of the present invention.

Optical element 7610 may comprise, for example glass, plastic or othermaterials transparent to a wavelength of light emitted by light engine7310. In some embodiments of the present invention, one or more portionsor all of the surfaces 7615 of optical element 7610 may be reflective toa wavelength of light emitted by light engine 7310. Such reflectivitymay be achieved by the application of a reflective coating over all ofor portions of surfaces 7615 of optical element 7610. For example areflective coating may comprise silver, gold aluminum or the like. Insome embodiments of this aspect of the present invention, the reflectivecoating may comprise a plurality of layers. In other examples thereflectivity may be achieved using a Bragg reflector.

In some embodiments of the present invention, optical element 7610 mayhave an index of refraction in the range of about 1 to about 3. In someembodiments of the invention optical element 7610 may have an index ofrefraction matching that of fill material 7625 or may have an index ofrefraction that may provide an index matching layer between fillmaterial 7625 and that of the space outside of the lamp (index ofrefraction is about 1 of air).

In some embodiments of the present invention optical element 7610 maycomprise a single optical element. However this is not a limitation ofthe present invention and in other embodiments optical element 7610 maycomprise a plurality of elements. In some embodiments of the presentinvention optical element 7610 may be molded to provide a relatively lowcost optical element.

In some embodiments of the present invention, optical element 7610 maybe attached directly to mounting element 7332 using, for exampleadhesive, glue or other means, or optical element may be positionedadjacent to mounting element 7332 by other means, for example a clamp orother mechanical support. In some embodiments of the invention a portionof housing 7390 may be attached to optical element 7610 and said portionof housing 7390 may be mechanically or otherwise attached to mountingelement 7332 and/or other portions of housing 7390, resulting in thecoupling of optical element 7610 to light engine 7310. Optical element7610 may have one or more cavities 7620 into which light engine 7310 maybe positioned and which may completely or partially surround lightengine 7310. Contact areas on light engine 7310 may be electricallycoupled to conductive elements within cavity 7620 or on mounting element7332 to permit eventual coupling to electronics module 7330.

After positioning of optical element 7610 on mounting element 7332 suchthat light engine 7310 may be within or partially within cavity 7620,cavity 7620 may be filled with a fill material 7625 with an appropriateindex of refraction. Fill material 7625 may also be called fillermaterial. In some embodiments of this aspect of the invention fillmaterial 7625 may have an index of refraction matching that of opticalelement 7610, and in other cases fill material 7625 may have an index ofrefraction matching that may provide an index matching layer betweenlight engine 7310 and optical element 7610. In some embodiments of thisaspect of the invention, fill material 7625 may contain light conversionmaterial 1810, however this is not a limitation of the present inventionand in other embodiments light conversion material 1810 may be part oflight engine 7310 or may be part of the optics module 7360 or somecombination of these examples. Optical element 7610 and/or optic module7630 may be attached to support element 7332, thus creating a sturdyassembly comprising optics module 7360 and light engine 7310.

In some embodiments of the present invention, cavity 7620 may be filledwith fill material 7625 using ports 7630 and 7640. Ports 7630 and 7640may provide access to the interior of cavity 7620 after optical element7610 is coupled to light engine 7310. A source of fill material 7625 maybe coupled to port 7630 and a source of vacuum may be coupled to port7640, wherein fill material 7625 may be drawn through port 7630, cavity7620 and port 7640, resulting in a complete filling of cavity 7620 withfill material 7625. Ports 7630 and 7640 may be de-coupled from thesource of fill material 7625 and vacuum respectively and fill material7625 may remain in and completely fill cavity 7620. In some embodimentsof this aspect of the invention fill material 7625 may be cured throughthe application of heat, optical radiation, for example UV, or othermeans.

In some embodiments of the present invention, different materials in theoptical path of the light from light engine 7310 to the space outside ofthe lamp may have refractive index changing as a function of distancefrom the light engine. In one example, filler material 7625 may haverefractive index graded from a value matching or close to that of thematerial of light engine 7310 or that of layer structure 750 (FIG. 20)to a value matching or close to that of the material comprising opticalelement 7610. This may provide reduced optical losses at the interfacebetween light engine 7310 and filler material 7625 and at the interfacebetween filler material 7625 and optical element 7610. In someembodiments of the present invention, optical element 7610 may have agraded refractive index, and in some embodiments may be graded from avalue matching or close to that of the material comprising light engine7310 (or that comprising layer structure 750 (FIG. 20)) to a valuematching or close to that of the material comprising optical element7610.

In some embodiments of the present invention, one or more surfaces or aportion of one or more surfaces of optical element 7610 may be shaped toprovide a desired light distribution. For example the surface from whichthe light exits optical element 7610 may comprise a lens or a portion ofa lens. In some embodiments of the present invention, one or moresurfaces or a portion of one or more surfaces of optical element 7610may be etched, patterned, frosted, or otherwise modified to provide acertain characteristic light output. In some embodiments of the presentinvention, one or more surfaces or a portion of one or more surfaces ofoptical element 7610 may be patterned to form surface features designedto improve light extraction or to direct light out of the optics, forexample a photonic crystal. In some embodiments of the presentinvention, the surface from which light exits optical element 7610 mayalso be the exterior surface of the lamp through which light isemitted—in other words there may be no additional lenses, diffuserplates, interfaces or other optical elements, to cause additionaloptical losses, after the light exits optical element 7610. In someembodiments of the present invention, the light may be patterned in adirectional pattern, for example for use in down lights, where it may bedesirable for all of the light to exit the lamp in a directionalfashion. In this example, if a lamp in a down light emitsomnidirectionally or relatively omnidirectionally, a relativelysignificant portion may be absorbed within the fixture, reducing theusable light from that luminaire. However, this is not a limitation ofthe present invention and in other embodiments the light may exit theLED lamp of the present invention omnidirectionally or in any pattern orwith any distribution.

As shown in FIG. 73, optical module 7360 may be spaced apart fromhousing 7390 in one or more areas. In some embodiments of the presentinvention, passive convective cooling may be employed to draw air into aportion of lamp housing 7390, provide cooling for internal componentssuch as light engine 7310 and/or electronics module 7330, and thenexhaust the heated air out of the lamp towards the direction of base7398. In this fashion a circulation system may be set up, drawing coldair in from the bottom and exhausting hot air out the top.

In contrast to prior-art LED lamps, the LED lamp of the presentinvention starts with the light engine which may be optimized for use ina particular lamp. In conjunction with the integrated optical module andoptimized electronics, the lamp of the present invention may providerelatively improved performance at relatively lower cost than prior-artLED lamps.

A key area of differentiation and cost reduction is the manufacture ofthe ILT LED light engine. FIG. 77 compares the manufacturing process fora LED lamp of the present invention with that of a prior-art LED lamp.Both processes start with an epitaxial LED wafer comprising a substrateand epitaxial layers (similar to the semiconductor structure in FIG.20). In the conventional process, shown in FIG. 77A, step 7710 startswith the LED wafer. The LED wafer is then processed to make individualLEDs on the wafer in step 7720. The wafer is then singulated into LEDdie in step 7730 and the individual LED die are packaged in step 7740.The packaged LEDs are then assembled on the circuit board in step 7750and finally the lamp is assembled in step 7760. Lamp assembly maycomprise assembly of the electronics, optics, thermal management system,LEDs on the circuit board into the lamp housing.

In the LED lamp of the present invention all of the steps of takingapart, packaging and assembling the packaged LEDs may be eliminated bythe fabrication and use of the light engine. In some embodiments of thepresent invention, several hundred light engines may be fabricatedsimultaneously on each wafer using standard IC processing techniques andtools. Each light engine is complete after wafer singulation. Anexemplary process for a LED lamp of the present invention is shown inFIG. 77B. Step 7770 starts with the LED wafer. The LED wafer is thenprocessed to make light engines on the wafer in step 7780. The wafer isthen singulated into completed light engines in step 7785 and then thelamp is assembled in step 7790. In some embodiments of the presentinvention lamp assembly may be relatively simplified and be able to beperformed at a relatively lower cost compared to the process for theprior-art LED lamp because of the modular nature of the LED lamp of thepresent invention.

In some embodiments of the present invention relatively large costsavings may be possible, resulting from a reduction in the number ofprocessing steps, elimination of the LED packages (which often cost asmuch as or more than the LED die) and elimination of the circuit boardand assembly steps. In some embodiments of the present invention, thelight engine of the present invention may use about 2× to about 3× morewafer area than the combined wafer area in the packaged LEDs used inprior-art LED lamps, for a similar light output. However, this cost ofthis additional area occurs at the wafer level, which is relatively lessexpensive than further downstream at the packaged LED level. In someembodiments of the present invention the light engine of the presentinvention may cost about 8× to about 10× less to manufacture than thelight emitting assembly (LEDs+circuit board+assembly cost) of aprior-art LED lamp.

The LED lamp of the present invention is designed to be assembled in amodular fashion. The light engine module may be attached to the opticsmodule. The light engine and optics sub-assembly may then be mountedtogether with the electronics module on the thermal management module.This complete assembly may then be mounted in the lamp housing. Becauseof the relatively low level of generated heat, the thermal managementsystem may be quite simple, for example consisting of a relativelymodest heat sink or in some embodiments of the present invention, theLED lamp housing itself. Overall, the LED lamp of the present inventionhas fewer components, higher performance and reduced assembly costs.After lamp assembly, the cost to manufacture a LED lamp of the presentinvention may be about 4× to about 6× less than the cost to manufacturea prior-art LED lamp.

FIG. 78 shows a comparison of the optical system in a prior-art LED lamp(FIG. 78A) and a LED lamp of the present invention (FIG. 78B). LED lampsmay require an optical system to diffuse the light emitted by the LEDsand provide the required light distribution pattern. Significant lossesin optics may occur at interfaces, because only part of the light istransmitted, while the remainder is reflected back and may be absorbed,generating heat. The larger the number of interfaces the light has totraverse, the lower the optical efficiency may be.

In the prior-art LED lamp (FIG. 78A) a plurality of packaged LEDs 7810may be positioned away from a lens 7815. The light emitted from each LEDdie inside each package must traverse 4 interfaces, including (1) die toencapsulant, (2) encapsulant to air, (3) air to lens, and (4) lens toair.

In contrast, in the approach of the present invention using an opticalelement optically coupled to the light engine as discussed above inreference to FIG. 76 the number of interfaces may only be about 2.Optical element 7610 may comprise a material transparent to a wavelengthof light emitted by the light engine, for example glass, and may becoupled to light engine 7310 with an index matching material (not shownin FIG. 78), as discussed above. In some embodiments of the presentinvention the optical efficiency may be about 10% to about 20% higherthan achievable using the prior-art approach.

Another aspect of optical losses is related to the etendue (etenduerefers to how “spread out” the light is in area and angle) of thesystem. The result of this is that one can only, without loss, capturelight radiated within a certain spatial distribution for a given opticaldesign. If the etendue is too large, optical losses will occur,decreasing the optical efficiency. In the LED lamp of the presentinvention, the light emitting area of the light engine may be in therange of about 3 mm×3 mm to about 7 mm×7 mm, which is relatively muchsmaller than the area covered by a plurality of packaged LEDs in theprior-art LED lamp approach. In some embodiments of the presentinvention the optical efficiency may be about 10% to about 20% higherthan achievable using the prior-art approach.

In some embodiments of the present invention, a large area modular lampmay be formed, comprising a plurality of the light engines, and optics,using either a single electronics and thermal management system ormultiple electronics and/or thermal management systems. Such a lamp maybe used in applications in which a very large total light output (morethan 10,000 lm or more than 20,000 lm) is required. Examples of suchlamps may include street lights, parking lights, or large area ceilinglight (say 1×1 foot) in large rooms. A schematic example of such amodular lamp is shown in FIG. 3.

In some embodiments of the present invention, a large area modular lampmay be formed, comprising a plurality of light engines, and opticalelements, using either a single electronics and thermal managementsystem or a plurality of electronics and/or thermal management systems.Such a lamp may be used in applications in which a relatively very largetotal light output (more than about 10,000 lm or more than about 20,000lm) may be required. Examples of such lamps may include street lights,parking lights, or large area ceiling light (for example with a size ofabout 1 ft×about 1 ft) in relatively large rooms.

FIG. 79 is a cross-sectional view of a portion of an exemplary largearea modular LED lamp in accordance with an embodiment of the presentinvention. FIG. 80 is a view of the structure of FIG. 79 from the lightemitting side of the structure and FIG. 79 is a cross-sectional viewtaken along section line 79-79 of FIG. 80. The example shown in FIG. 3comprises a 3×3 modular array of light engines 7310 with opticalelements 7610 disposed on a single support element 7332. Not shown inFIG. 79 or 80 are the electronics module, the housing and any necessaryadditional thermal management system.

The example shown in FIG. 80 comprises optical element 7610 with arectangular shape, however this is not a limitation of the presentinvention and in other embodiments optical element 7610 may have anyshape. The example shown in FIG. 80 comprises an array of 3×3 lightengines 7310, however this is not a limitation of the present inventionand in other embodiments any number or arrangement of light engines andoptical elements 7610 may be used. The example shown in FIG. 80comprises an array with equal number of rows and columns of lightengines 7310, however this is not a limitation of the present inventionand in other embodiments any number of light engines may be in used inboth rows and columns. The example shown in FIG. 80 comprise an arraywith equal number of rows and columns of light engines 7310, howeverthis is not a limitation of the present invention and in otherembodiments any number of light engines may be in used in both rows andcolumns. The example shown in FIG. 80 comprises a regular periodic arrayof light engines 7310 and optical elements 7610, however this is not alimitation of the present invention and in other embodiments one or morelight engines 7310 and/or one or more optical elements 7610 may be inany random position. The example shown in FIG. 80 comprises a pluralityof light engines 7310 and optical elements 7610, wherein each lightengine 7630 may be optically coupled to one optical element 7610,however this is not a limitation of the present invention and in otherembodiments one or more light engines 7310 may be optically coupled toone or more optical elements 7610 or one or more optical elements 7610may be optically coupled to one or more light engines 7310.

Several examples of LED units, light engines and LED lamps emitting atdifferent wavelengths have been presented herein, however, it should berecognized that numerous methods and materials may be used to makeproduce light emission at multiple wavelengths or with an engineeredspectral light distribution and/or characteristic, and these examples donot represent limitations on the invention.

It is to be understood that each of fabrication sequences discussedherein and shown in the figures represents only certain embodiments andthat the specification of specific steps and an order for those steps isexemplary rather than limiting. In particular, in each case, there areembodiments in which some of the specified steps might not be performed,embodiments in which additional steps might be performed, andembodiments in which specifically identified steps might be performed ina different order than is shown.

INDUSTRIAL APPLICABILITY

The present invention has industrial applicability for a wide range oflighting applications including, for example, automotive, architectural,backlighting of displays and signage and general lighting.

1-22. (canceled)
 23. A lighting system comprising: an electricallyinsulating carrier having a plurality of conductive elements disposedthereon; disposed over the carrier, a light-emitting array comprising aplurality of light-emitting strings electrically connected in parallel,each light-emitting string comprising a plurality of electricallyconnected light-emitting diodes (LEDs), each LED having at least twoelectrical contacts, wherein each electrical contact is electricallyconnected to a conductive element by an electrical connection comprisingat least one of a conductive adhesive or a solder; at least one powersource for providing power to the light-emitting strings; and one ormore cross connections each electrically connecting portions of two ormore light-emitting strings, each electrically connected portion beingdisposed between a pair of LEDs.
 24. The lighting system of claim 23,wherein at least one cross connection electrically connects togetherportions of all of the light-emitting strings.
 25. The lighting systemof claim 23, wherein (i) the one or more cross connections comprise aplurality of cross connections, and (ii) for one or more light-emittingstrings, each different portion thereof disposed between a differentpair of LEDs is electrically connected to a different cross connection.26. The lighting system of claim 23, wherein (i) the one or more crossconnections comprise a plurality of cross connections, and (ii) for eachlight-emitting string, each different portion thereof disposed between adifferent pair of LEDs is electrically connected to a different crossconnection.
 27. The lighting system of claim 23, wherein the LEDs withineach light-emitting string are electrically connected in series.
 28. Thelighting system of claim 27, wherein (i) each light-emitting stringcontains the same number of LEDs, (ii) the one or more cross connectionscomprise a plurality of cross connections, and (iii) for eachlight-emitting string, each different portion thereof disposed betweeneach different pair of LEDs is electrically connected to a differentcross connection.
 29. The lighting system of claim 23, wherein (i) theone or more cross connections comprise a plurality of cross connections,and (ii) the plurality of light-emitting strings and plurality of crossconnections collectively form an interconnected grid of LEDs, such that(a) for each light-emitting string, an electrical connection to adifferent cross connection is disposed between each pair of LEDs, and(b) each cross connection is electrically connected to all of thelight-emitting strings.
 30. The system of claim 23, wherein theelectrically insulating carrier comprises a polymeric material.
 31. Thesystem of claim 23, wherein at least one LED comprises a packaged LED.32. The system of claim 31, wherein the packaged LED comprises alight-conversion material.
 33. The system of claim 32, wherein thelight-conversion material comprises a phosphor.
 34. The system of claim23, wherein at least one LED comprises a bare-die LED.
 35. The system ofclaim 34, further comprising a light-conversion material disposed overat least a portion of the bare-die LED.
 36. The system of claim 35,wherein the light-conversion material comprises a phosphor.
 37. Thesystem of claim 23, wherein the electrically insulating carrier isflexible.
 38. The system of claim 23, further comprising alight-conversion material disposed in or over at least one of the LEDs,wherein the electrically insulating carrier is reflective to at leastone of (i) a wavelength of light emitted by at least one of the LEDs or(ii) a wavelength of light emitted by the light-conversion material. 39.The system of claim 23, further comprising a light-conversion materialdisposed in or over at least one of the LEDs, wherein the electricallyinsulating carrier is substantially transparent to at least one of (i) awavelength of light emitted by at least one of the LEDs or (ii) awavelength of light emitted by the light-conversion material.
 40. Thesystem of claim 23, further comprising, disposed on the electricallyinsulating carrier, circuitry for controlling current supplied to theLEDs.
 41. The system of claim 40, wherein the circuitry comprises one ormore resistors.
 42. The system of claim 40, wherein the circuitrycomprises one or more transistors.
 43. The system of claim 40, whereinthe circuitry comprises at least one resistor and at least onetransistor.
 44. The system of claim 40, wherein the circuitry comprisesat least one integrated circuit.
 45. The system of claim 23, furthercomprising, disposed on the electrically insulating carrier, a pluralityof circuits each for controlling current supplied to one of thelight-emitting strings.
 46. The system of claim 45, wherein each circuitcomprises one or more resistors.
 47. The system of claim 45, whereineach circuit comprises one or more transistors.
 48. The system of claim45, wherein each circuit comprises at least one resistor and at leastone transistor.
 49. The system of claim 23, wherein at least one of theLEDs comprises a semiconductor material comprising at least one ofsilicon, SiC, GaAs, Al_(x)In_(y)Ga_(1-x-y)P_(z)N_(t)As_(1-t-z),Al_(x)In_(y)Ga_(1-x-y)N, ZnO, or mixtures or compounds thereof.
 50. Thesystem of claim 23, wherein at least one of the LEDs emits UV, blue, orgreen light.
 51. The system of claim 23, wherein at least one of theLEDs comprises a light-conversion material disposed therein or thereon,at least one of (i) light emitted from the light-conversion material or(ii) a mixture of light emitted from the at least one of the LEDs andthe light-conversion material being white light.
 52. The system of claim23, further comprising an array of optical elements each associated withat least one LED, the array of optical elements at least one of focusingor shaping light from the LEDs to a desired illumination pattern. 53.The system of claim 52, wherein each optical element is opticallycoupled to at least one LED with no interface to air therebetween. 54.The system of claim 23, further comprising, electrically connected tothe plurality of light-emitting strings, electrical circuitry forselectively turning off various ones of the light-emitting strings,thereby dimming a light output of the light-emitting array, withoutaltering a level of drive current supplied to the LEDs.
 55. The systemof claim 23, wherein at least one first light-emitting string emitslight having a color, color temperature, intensity, efficiency, colorrendering index, or spectral light distribution different from a color,color temperature, intensity, efficiency, color rendering index, orspectral light distribution of at least one second light-emittingstring.
 56. The system of claim 55, wherein the LEDs of the at least onefirst light-emitting string are substantially identical to the LEDs ofthe at least one second light-emitting string.
 57. The system of claim55, wherein at least one of the LEDs of the at least one firstlight-emitting string is associated with a first light conversionmaterial having a first optical characteristic, and at least one of theLEDs of the at least one second light-emitting string is associated witha second light conversion material having a second opticalcharacteristic different from the first optical characteristic.
 58. Thesystem of claim 55, wherein at least one of the LEDs of the at least onefirst light-emitting string is associated with an optical element of afirst type, and at least one of the LEDs of the at least one secondlight-emitting string is associated with an optical element of a secondtype different from the first type.
 59. The system of claim 23, wherein:the light-emitting array comprises (i) a first group of one or morelight-emitting strings, and (ii) a second group of one or morelight-emitting strings different from the first group, activation of thefirst group and deactivation of the second group produces light having afirst color, color temperature, intensity, efficiency, color renderingindex, or spectral light distribution, and activation of the secondgroup and deactivation of the first group produces light having a secondcolor, color temperature, intensity, efficiency, color rendering index,or spectral light distribution different from the first color, colortemperature, intensity, efficiency, color rendering index, or spectrallight distribution.
 60. The system of claim 23, wherein: thelight-emitting array comprises a first group of one or morelight-emitting strings and, associated with at least one of the LEDs ofthe first group, a first optical element of a first type, thelight-emitting array comprises a second group, different from the firstgroup, of one or more light-emitting strings and, associated with atleast one of the LEDs of the second group, a second optical element of asecond type different from the first type, activation of the first groupand deactivation of the second group produces light having a firstcolor, color temperature, intensity, efficiency, color rendering index,or spectral light distribution, and activation of the second group anddeactivation of the first group produces light having a second color,color temperature, intensity, efficiency, color rendering index, orspectral light distribution different from the first color, colortemperature, intensity, efficiency, color rendering index, or spectrallight distribution.
 61. The system of claim 23, wherein: thelight-emitting array comprises a first group of one or morelight-emitting strings and, associated with at least one of the LEDs ofthe first group, a first light-conversion material having a firstoptical characteristic, the light-emitting array comprises a secondgroup, different from the first group, of one or more light-emittingstrings and, associated with at least one of the LEDs of the secondgroup, a second light-conversion material having a second opticalcharacteristic different from the first optical characteristic,activation of the first group and deactivation of the second groupproduces light having a first color, color temperature, intensity,efficiency, color rendering index, or spectral light distribution, andactivation of the second group and deactivation of the first groupproduces light having a second color, color temperature, intensity,efficiency, color rendering index, or spectral light distributiondifferent from the first color, color temperature, intensity,efficiency, color rendering index, or spectral light distribution. 62.The system of claim 23, wherein at least one LED comprises a substratethat is substantially transparent to a wavelength of light emitted bythe at least one LED.
 63. The system of claim 23, wherein at least oneLED comprises a light-conversion material disposed therein or thereon,the at least one LED comprising a substrate that is substantiallytransparent to at least one of (i) a wavelength of light emitted by atleast one LED or (ii) a wavelength of light emitted by thelight-conversion material.
 64. The system of claim 23, wherein theplurality of light-emitting strings comprises (i) a first light-emittingstring in which at least one LED comprises a light-conversion material,and (ii) a second light-emitting string, different from the firstlight-emitting string, in which at least one LED lacks alight-conversion material.
 65. The system of claim 23, wherein theplurality of light-emitting strings comprises a first light-emittingstring configured for emission of white light and a second lightemitting string, different from the first light-emitting string,configured for emission of red light.
 66. The system of claim 23,further comprising: a second electrically insulating carrier having aplurality of conductive elements disposed thereon; and disposed over thesecond electrically insulating carrier, a light-emitting arraycomprising a plurality of light-emitting strings, each light-emittingstring comprising a plurality of LEDs electrically connected in series,wherein (i) the strings on the electrically insulating carrier producelight having a first color, color temperature, intensity, efficiency,color rendering index, or spectral light distribution, and (ii) thestrings on the second electrically insulating carrier produce lighthaving a second color, color temperature, intensity, efficiency, colorrendering index, or spectral light distribution different from the firstcolor, color temperature, intensity, efficiency, color rendering index,or spectral light distribution.
 67. The system of claim 23, furthercomprising: a second electrically insulating carrier having a pluralityof conductive elements disposed thereon; and disposed over the secondelectrically insulating carrier, a light-emitting array comprising aplurality of light-emitting strings, each light-emitting stringcomprising a plurality of LEDs electrically connected in series, wherein(i) the strings on the electrically insulating carrier produce lighthaving a first color, color temperature, intensity, efficiency, colorrendering index, or spectral light distribution, and (ii) the strings onthe second electrically insulating carrier produce light having a secondcolor, color temperature, intensity, efficiency, color rendering index,or spectral light distribution substantially the same as the firstcolor, color temperature, intensity, efficiency, color rendering index,or spectral light distribution.
 68. The system of claim 23, wherein (i)the plurality of conductive elements form a two-dimensional gridextending in first and second directions, (ii) conductive elementsextending in the first direction electrically connect LEDs in series,and (iii) conductive elements extending in the second directionelectrically interconnect conductive elements extending in the firstdirection.